Finite automaton that recognizes the empty language $emptyset$











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Since the language $L = emptyset$ is regular, there must be a finite automaton that recognizes it. However, I'm not exactly sure how one would be constructed. I feel like the answer is trivial. Can someone help me out?










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  • Write "This automaton is...." or "These automata are....". (I fixed this in the question.)
    – Michael Hardy
    Mar 26 '13 at 3:24















up vote
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Since the language $L = emptyset$ is regular, there must be a finite automaton that recognizes it. However, I'm not exactly sure how one would be constructed. I feel like the answer is trivial. Can someone help me out?










share|cite|improve this question
























  • Write "This automaton is...." or "These automata are....". (I fixed this in the question.)
    – Michael Hardy
    Mar 26 '13 at 3:24













up vote
10
down vote

favorite
5









up vote
10
down vote

favorite
5






5





Since the language $L = emptyset$ is regular, there must be a finite automaton that recognizes it. However, I'm not exactly sure how one would be constructed. I feel like the answer is trivial. Can someone help me out?










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Since the language $L = emptyset$ is regular, there must be a finite automaton that recognizes it. However, I'm not exactly sure how one would be constructed. I feel like the answer is trivial. Can someone help me out?







computer-science formal-languages automata






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edited Mar 30 '13 at 0:26









Tara B

4,8601436




4,8601436










asked Mar 25 '13 at 22:32









user68486

51113




51113












  • Write "This automaton is...." or "These automata are....". (I fixed this in the question.)
    – Michael Hardy
    Mar 26 '13 at 3:24


















  • Write "This automaton is...." or "These automata are....". (I fixed this in the question.)
    – Michael Hardy
    Mar 26 '13 at 3:24
















Write "This automaton is...." or "These automata are....". (I fixed this in the question.)
– Michael Hardy
Mar 26 '13 at 3:24




Write "This automaton is...." or "These automata are....". (I fixed this in the question.)
– Michael Hardy
Mar 26 '13 at 3:24










4 Answers
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11
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One state, non-accepting, and no transitions. (That’s an NFA; if you want a DFA, have one transition from the state to itself for each letter of whatever alphabet is specified.)






share|cite|improve this answer

















  • 1




    Can a finite automata have no accept states at all?
    – user68486
    Mar 25 '13 at 22:40






  • 2




    @user68486: Yes, it can: the set of acceptor states can be any subset of the set of states.
    – Brian M. Scott
    Mar 25 '13 at 22:42










  • Can you please elaborate, why the NFA can have no transitions, but the DFA must have a transition for every letter in the alphabet?
    – de_dust
    Oct 19 '17 at 9:24










  • for a moment I felt we shouldnt need any state (invisible FA :p)...seems thats not allowed...
    – anir
    Dec 23 '17 at 15:57


















up vote
6
down vote













You have only one state $s$ that is initial, but not accepting with loops $s overset{alpha}{rightarrow} s$ for any letter $alpha in Sigma$ (with non-deterministic automaton you can even skip the loops, i.e. the transition relation would be empty).



I hope this helps ;-)






share|cite|improve this answer




























    up vote
    1
    down vote













    Given language is "empty language".We have to construct a finite automata for this language.In general we consider "the construction of finite automata" as "the construction of DFA".So....{Let us assume input symbol as 'a' and 'b'}



    (a)If we take one state(initial state) and don't show any transition of any input symbol over this state,then this structure will not be a DFA because in a DFA there should be a transition of all input symbol over each state.
    (b)If we take one state(initial state) and show the transition of both input symbol 'a' and 'b' over this state, then also this will not be a DFA because there should be a final state.
    (c)If we take one state(initial state) and show the transition of both input symbol 'a' and 'b' over this state,and making this state final also then this FA will not be acceptor of "empty language".
    (d)If we take one initial state 'A'(not making final it) showing the transition of both input symbol over 'A' itself AND taking one another state 'B'(as final)showing the transition of both input symbol over the "transion edge" from final state 'B' to initial state 'A'('B'is UNREACHABLE STATE here).Then this structure will be a DFA but not minimal DFA because in minimal DFA we remove UNREACHABLE STATE.
    (e)similarly we cannot take concept of dead state in construction of minimal DFA.



    SO NOW THE EXACT SOLUTION IS :-



    " TAKE ONE INITIAL STATE 'A'(not making final it) and ONE ANOTHER STATE 'B'(making it final) and SHOW transition of both input symbol 'a' and 'b' over both state A' and 'B'. BUT don't connect both states with any transition edge.
    This is the desired minimal DFA which accepts "empty language".






    share|cite|improve this answer




























      up vote
      1
      down vote













      This will be the DFA



      This is the DFA that iterates over (0|1)* but does not accept anything (not even empty string).






      share|cite|improve this answer























      • You've just said "accept empty string" and then "does not accept anything". Can you explain it better?
        – JB-Franco
        Mar 15 '17 at 22:24






      • 1




        @JB-Franco Acceptance of empty thing == not accepting anything! I think you are aware of "empty language", which means "no string", So to rephrase, "accepts empty string" == "accepts no string" == "does not accepts anything". If you still have problems, please comment.
        – lU5er
        Mar 17 '17 at 12:17










      • Thanks! - The fact you have explained in the above about DFA accepting empty string, can be related to what I have asked here: Why in a DFA the empty string distinguishes any accept state from any reject state?
        – JB-Franco
        Mar 17 '17 at 19:41








      • 1




        This answer is wrong because "accepts empty string" and "accepts no string" are not the same! The NFA with only one state and no transitions accepts no strings if the state is non-accepting, and the empty string (but no other strings) if the state is accepting. Similarly, a DFA can accept only the empty string and no others by having a start state which is accepting and then all transitions point to a non-accepting trap state like the one in this answer.
        – Benjamin Cosman
        May 29 '17 at 16:13












      • @BenjaminCosman, answer me one thing, what do you mean by empty string?
        – lU5er
        May 30 '17 at 17:25











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      4 Answers
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      4 Answers
      4






      active

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      active

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      active

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      up vote
      11
      down vote













      One state, non-accepting, and no transitions. (That’s an NFA; if you want a DFA, have one transition from the state to itself for each letter of whatever alphabet is specified.)






      share|cite|improve this answer

















      • 1




        Can a finite automata have no accept states at all?
        – user68486
        Mar 25 '13 at 22:40






      • 2




        @user68486: Yes, it can: the set of acceptor states can be any subset of the set of states.
        – Brian M. Scott
        Mar 25 '13 at 22:42










      • Can you please elaborate, why the NFA can have no transitions, but the DFA must have a transition for every letter in the alphabet?
        – de_dust
        Oct 19 '17 at 9:24










      • for a moment I felt we shouldnt need any state (invisible FA :p)...seems thats not allowed...
        – anir
        Dec 23 '17 at 15:57















      up vote
      11
      down vote













      One state, non-accepting, and no transitions. (That’s an NFA; if you want a DFA, have one transition from the state to itself for each letter of whatever alphabet is specified.)






      share|cite|improve this answer

















      • 1




        Can a finite automata have no accept states at all?
        – user68486
        Mar 25 '13 at 22:40






      • 2




        @user68486: Yes, it can: the set of acceptor states can be any subset of the set of states.
        – Brian M. Scott
        Mar 25 '13 at 22:42










      • Can you please elaborate, why the NFA can have no transitions, but the DFA must have a transition for every letter in the alphabet?
        – de_dust
        Oct 19 '17 at 9:24










      • for a moment I felt we shouldnt need any state (invisible FA :p)...seems thats not allowed...
        – anir
        Dec 23 '17 at 15:57













      up vote
      11
      down vote










      up vote
      11
      down vote









      One state, non-accepting, and no transitions. (That’s an NFA; if you want a DFA, have one transition from the state to itself for each letter of whatever alphabet is specified.)






      share|cite|improve this answer












      One state, non-accepting, and no transitions. (That’s an NFA; if you want a DFA, have one transition from the state to itself for each letter of whatever alphabet is specified.)







      share|cite|improve this answer












      share|cite|improve this answer



      share|cite|improve this answer










      answered Mar 25 '13 at 22:38









      Brian M. Scott

      453k38504904




      453k38504904








      • 1




        Can a finite automata have no accept states at all?
        – user68486
        Mar 25 '13 at 22:40






      • 2




        @user68486: Yes, it can: the set of acceptor states can be any subset of the set of states.
        – Brian M. Scott
        Mar 25 '13 at 22:42










      • Can you please elaborate, why the NFA can have no transitions, but the DFA must have a transition for every letter in the alphabet?
        – de_dust
        Oct 19 '17 at 9:24










      • for a moment I felt we shouldnt need any state (invisible FA :p)...seems thats not allowed...
        – anir
        Dec 23 '17 at 15:57














      • 1




        Can a finite automata have no accept states at all?
        – user68486
        Mar 25 '13 at 22:40






      • 2




        @user68486: Yes, it can: the set of acceptor states can be any subset of the set of states.
        – Brian M. Scott
        Mar 25 '13 at 22:42










      • Can you please elaborate, why the NFA can have no transitions, but the DFA must have a transition for every letter in the alphabet?
        – de_dust
        Oct 19 '17 at 9:24










      • for a moment I felt we shouldnt need any state (invisible FA :p)...seems thats not allowed...
        – anir
        Dec 23 '17 at 15:57








      1




      1




      Can a finite automata have no accept states at all?
      – user68486
      Mar 25 '13 at 22:40




      Can a finite automata have no accept states at all?
      – user68486
      Mar 25 '13 at 22:40




      2




      2




      @user68486: Yes, it can: the set of acceptor states can be any subset of the set of states.
      – Brian M. Scott
      Mar 25 '13 at 22:42




      @user68486: Yes, it can: the set of acceptor states can be any subset of the set of states.
      – Brian M. Scott
      Mar 25 '13 at 22:42












      Can you please elaborate, why the NFA can have no transitions, but the DFA must have a transition for every letter in the alphabet?
      – de_dust
      Oct 19 '17 at 9:24




      Can you please elaborate, why the NFA can have no transitions, but the DFA must have a transition for every letter in the alphabet?
      – de_dust
      Oct 19 '17 at 9:24












      for a moment I felt we shouldnt need any state (invisible FA :p)...seems thats not allowed...
      – anir
      Dec 23 '17 at 15:57




      for a moment I felt we shouldnt need any state (invisible FA :p)...seems thats not allowed...
      – anir
      Dec 23 '17 at 15:57










      up vote
      6
      down vote













      You have only one state $s$ that is initial, but not accepting with loops $s overset{alpha}{rightarrow} s$ for any letter $alpha in Sigma$ (with non-deterministic automaton you can even skip the loops, i.e. the transition relation would be empty).



      I hope this helps ;-)






      share|cite|improve this answer

























        up vote
        6
        down vote













        You have only one state $s$ that is initial, but not accepting with loops $s overset{alpha}{rightarrow} s$ for any letter $alpha in Sigma$ (with non-deterministic automaton you can even skip the loops, i.e. the transition relation would be empty).



        I hope this helps ;-)






        share|cite|improve this answer























          up vote
          6
          down vote










          up vote
          6
          down vote









          You have only one state $s$ that is initial, but not accepting with loops $s overset{alpha}{rightarrow} s$ for any letter $alpha in Sigma$ (with non-deterministic automaton you can even skip the loops, i.e. the transition relation would be empty).



          I hope this helps ;-)






          share|cite|improve this answer












          You have only one state $s$ that is initial, but not accepting with loops $s overset{alpha}{rightarrow} s$ for any letter $alpha in Sigma$ (with non-deterministic automaton you can even skip the loops, i.e. the transition relation would be empty).



          I hope this helps ;-)







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Mar 25 '13 at 22:39









          dtldarek

          32k74399




          32k74399






















              up vote
              1
              down vote













              Given language is "empty language".We have to construct a finite automata for this language.In general we consider "the construction of finite automata" as "the construction of DFA".So....{Let us assume input symbol as 'a' and 'b'}



              (a)If we take one state(initial state) and don't show any transition of any input symbol over this state,then this structure will not be a DFA because in a DFA there should be a transition of all input symbol over each state.
              (b)If we take one state(initial state) and show the transition of both input symbol 'a' and 'b' over this state, then also this will not be a DFA because there should be a final state.
              (c)If we take one state(initial state) and show the transition of both input symbol 'a' and 'b' over this state,and making this state final also then this FA will not be acceptor of "empty language".
              (d)If we take one initial state 'A'(not making final it) showing the transition of both input symbol over 'A' itself AND taking one another state 'B'(as final)showing the transition of both input symbol over the "transion edge" from final state 'B' to initial state 'A'('B'is UNREACHABLE STATE here).Then this structure will be a DFA but not minimal DFA because in minimal DFA we remove UNREACHABLE STATE.
              (e)similarly we cannot take concept of dead state in construction of minimal DFA.



              SO NOW THE EXACT SOLUTION IS :-



              " TAKE ONE INITIAL STATE 'A'(not making final it) and ONE ANOTHER STATE 'B'(making it final) and SHOW transition of both input symbol 'a' and 'b' over both state A' and 'B'. BUT don't connect both states with any transition edge.
              This is the desired minimal DFA which accepts "empty language".






              share|cite|improve this answer

























                up vote
                1
                down vote













                Given language is "empty language".We have to construct a finite automata for this language.In general we consider "the construction of finite automata" as "the construction of DFA".So....{Let us assume input symbol as 'a' and 'b'}



                (a)If we take one state(initial state) and don't show any transition of any input symbol over this state,then this structure will not be a DFA because in a DFA there should be a transition of all input symbol over each state.
                (b)If we take one state(initial state) and show the transition of both input symbol 'a' and 'b' over this state, then also this will not be a DFA because there should be a final state.
                (c)If we take one state(initial state) and show the transition of both input symbol 'a' and 'b' over this state,and making this state final also then this FA will not be acceptor of "empty language".
                (d)If we take one initial state 'A'(not making final it) showing the transition of both input symbol over 'A' itself AND taking one another state 'B'(as final)showing the transition of both input symbol over the "transion edge" from final state 'B' to initial state 'A'('B'is UNREACHABLE STATE here).Then this structure will be a DFA but not minimal DFA because in minimal DFA we remove UNREACHABLE STATE.
                (e)similarly we cannot take concept of dead state in construction of minimal DFA.



                SO NOW THE EXACT SOLUTION IS :-



                " TAKE ONE INITIAL STATE 'A'(not making final it) and ONE ANOTHER STATE 'B'(making it final) and SHOW transition of both input symbol 'a' and 'b' over both state A' and 'B'. BUT don't connect both states with any transition edge.
                This is the desired minimal DFA which accepts "empty language".






                share|cite|improve this answer























                  up vote
                  1
                  down vote










                  up vote
                  1
                  down vote









                  Given language is "empty language".We have to construct a finite automata for this language.In general we consider "the construction of finite automata" as "the construction of DFA".So....{Let us assume input symbol as 'a' and 'b'}



                  (a)If we take one state(initial state) and don't show any transition of any input symbol over this state,then this structure will not be a DFA because in a DFA there should be a transition of all input symbol over each state.
                  (b)If we take one state(initial state) and show the transition of both input symbol 'a' and 'b' over this state, then also this will not be a DFA because there should be a final state.
                  (c)If we take one state(initial state) and show the transition of both input symbol 'a' and 'b' over this state,and making this state final also then this FA will not be acceptor of "empty language".
                  (d)If we take one initial state 'A'(not making final it) showing the transition of both input symbol over 'A' itself AND taking one another state 'B'(as final)showing the transition of both input symbol over the "transion edge" from final state 'B' to initial state 'A'('B'is UNREACHABLE STATE here).Then this structure will be a DFA but not minimal DFA because in minimal DFA we remove UNREACHABLE STATE.
                  (e)similarly we cannot take concept of dead state in construction of minimal DFA.



                  SO NOW THE EXACT SOLUTION IS :-



                  " TAKE ONE INITIAL STATE 'A'(not making final it) and ONE ANOTHER STATE 'B'(making it final) and SHOW transition of both input symbol 'a' and 'b' over both state A' and 'B'. BUT don't connect both states with any transition edge.
                  This is the desired minimal DFA which accepts "empty language".






                  share|cite|improve this answer












                  Given language is "empty language".We have to construct a finite automata for this language.In general we consider "the construction of finite automata" as "the construction of DFA".So....{Let us assume input symbol as 'a' and 'b'}



                  (a)If we take one state(initial state) and don't show any transition of any input symbol over this state,then this structure will not be a DFA because in a DFA there should be a transition of all input symbol over each state.
                  (b)If we take one state(initial state) and show the transition of both input symbol 'a' and 'b' over this state, then also this will not be a DFA because there should be a final state.
                  (c)If we take one state(initial state) and show the transition of both input symbol 'a' and 'b' over this state,and making this state final also then this FA will not be acceptor of "empty language".
                  (d)If we take one initial state 'A'(not making final it) showing the transition of both input symbol over 'A' itself AND taking one another state 'B'(as final)showing the transition of both input symbol over the "transion edge" from final state 'B' to initial state 'A'('B'is UNREACHABLE STATE here).Then this structure will be a DFA but not minimal DFA because in minimal DFA we remove UNREACHABLE STATE.
                  (e)similarly we cannot take concept of dead state in construction of minimal DFA.



                  SO NOW THE EXACT SOLUTION IS :-



                  " TAKE ONE INITIAL STATE 'A'(not making final it) and ONE ANOTHER STATE 'B'(making it final) and SHOW transition of both input symbol 'a' and 'b' over both state A' and 'B'. BUT don't connect both states with any transition edge.
                  This is the desired minimal DFA which accepts "empty language".







                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered Aug 10 '15 at 16:49









                  Salman Ahmad

                  111




                  111






















                      up vote
                      1
                      down vote













                      This will be the DFA



                      This is the DFA that iterates over (0|1)* but does not accept anything (not even empty string).






                      share|cite|improve this answer























                      • You've just said "accept empty string" and then "does not accept anything". Can you explain it better?
                        – JB-Franco
                        Mar 15 '17 at 22:24






                      • 1




                        @JB-Franco Acceptance of empty thing == not accepting anything! I think you are aware of "empty language", which means "no string", So to rephrase, "accepts empty string" == "accepts no string" == "does not accepts anything". If you still have problems, please comment.
                        – lU5er
                        Mar 17 '17 at 12:17










                      • Thanks! - The fact you have explained in the above about DFA accepting empty string, can be related to what I have asked here: Why in a DFA the empty string distinguishes any accept state from any reject state?
                        – JB-Franco
                        Mar 17 '17 at 19:41








                      • 1




                        This answer is wrong because "accepts empty string" and "accepts no string" are not the same! The NFA with only one state and no transitions accepts no strings if the state is non-accepting, and the empty string (but no other strings) if the state is accepting. Similarly, a DFA can accept only the empty string and no others by having a start state which is accepting and then all transitions point to a non-accepting trap state like the one in this answer.
                        – Benjamin Cosman
                        May 29 '17 at 16:13












                      • @BenjaminCosman, answer me one thing, what do you mean by empty string?
                        – lU5er
                        May 30 '17 at 17:25















                      up vote
                      1
                      down vote













                      This will be the DFA



                      This is the DFA that iterates over (0|1)* but does not accept anything (not even empty string).






                      share|cite|improve this answer























                      • You've just said "accept empty string" and then "does not accept anything". Can you explain it better?
                        – JB-Franco
                        Mar 15 '17 at 22:24






                      • 1




                        @JB-Franco Acceptance of empty thing == not accepting anything! I think you are aware of "empty language", which means "no string", So to rephrase, "accepts empty string" == "accepts no string" == "does not accepts anything". If you still have problems, please comment.
                        – lU5er
                        Mar 17 '17 at 12:17










                      • Thanks! - The fact you have explained in the above about DFA accepting empty string, can be related to what I have asked here: Why in a DFA the empty string distinguishes any accept state from any reject state?
                        – JB-Franco
                        Mar 17 '17 at 19:41








                      • 1




                        This answer is wrong because "accepts empty string" and "accepts no string" are not the same! The NFA with only one state and no transitions accepts no strings if the state is non-accepting, and the empty string (but no other strings) if the state is accepting. Similarly, a DFA can accept only the empty string and no others by having a start state which is accepting and then all transitions point to a non-accepting trap state like the one in this answer.
                        – Benjamin Cosman
                        May 29 '17 at 16:13












                      • @BenjaminCosman, answer me one thing, what do you mean by empty string?
                        – lU5er
                        May 30 '17 at 17:25













                      up vote
                      1
                      down vote










                      up vote
                      1
                      down vote









                      This will be the DFA



                      This is the DFA that iterates over (0|1)* but does not accept anything (not even empty string).






                      share|cite|improve this answer














                      This will be the DFA



                      This is the DFA that iterates over (0|1)* but does not accept anything (not even empty string).







                      share|cite|improve this answer














                      share|cite|improve this answer



                      share|cite|improve this answer








                      edited Jun 7 '17 at 23:17

























                      answered Dec 21 '16 at 20:46









                      lU5er

                      205111




                      205111












                      • You've just said "accept empty string" and then "does not accept anything". Can you explain it better?
                        – JB-Franco
                        Mar 15 '17 at 22:24






                      • 1




                        @JB-Franco Acceptance of empty thing == not accepting anything! I think you are aware of "empty language", which means "no string", So to rephrase, "accepts empty string" == "accepts no string" == "does not accepts anything". If you still have problems, please comment.
                        – lU5er
                        Mar 17 '17 at 12:17










                      • Thanks! - The fact you have explained in the above about DFA accepting empty string, can be related to what I have asked here: Why in a DFA the empty string distinguishes any accept state from any reject state?
                        – JB-Franco
                        Mar 17 '17 at 19:41








                      • 1




                        This answer is wrong because "accepts empty string" and "accepts no string" are not the same! The NFA with only one state and no transitions accepts no strings if the state is non-accepting, and the empty string (but no other strings) if the state is accepting. Similarly, a DFA can accept only the empty string and no others by having a start state which is accepting and then all transitions point to a non-accepting trap state like the one in this answer.
                        – Benjamin Cosman
                        May 29 '17 at 16:13












                      • @BenjaminCosman, answer me one thing, what do you mean by empty string?
                        – lU5er
                        May 30 '17 at 17:25


















                      • You've just said "accept empty string" and then "does not accept anything". Can you explain it better?
                        – JB-Franco
                        Mar 15 '17 at 22:24






                      • 1




                        @JB-Franco Acceptance of empty thing == not accepting anything! I think you are aware of "empty language", which means "no string", So to rephrase, "accepts empty string" == "accepts no string" == "does not accepts anything". If you still have problems, please comment.
                        – lU5er
                        Mar 17 '17 at 12:17










                      • Thanks! - The fact you have explained in the above about DFA accepting empty string, can be related to what I have asked here: Why in a DFA the empty string distinguishes any accept state from any reject state?
                        – JB-Franco
                        Mar 17 '17 at 19:41








                      • 1




                        This answer is wrong because "accepts empty string" and "accepts no string" are not the same! The NFA with only one state and no transitions accepts no strings if the state is non-accepting, and the empty string (but no other strings) if the state is accepting. Similarly, a DFA can accept only the empty string and no others by having a start state which is accepting and then all transitions point to a non-accepting trap state like the one in this answer.
                        – Benjamin Cosman
                        May 29 '17 at 16:13












                      • @BenjaminCosman, answer me one thing, what do you mean by empty string?
                        – lU5er
                        May 30 '17 at 17:25
















                      You've just said "accept empty string" and then "does not accept anything". Can you explain it better?
                      – JB-Franco
                      Mar 15 '17 at 22:24




                      You've just said "accept empty string" and then "does not accept anything". Can you explain it better?
                      – JB-Franco
                      Mar 15 '17 at 22:24




                      1




                      1




                      @JB-Franco Acceptance of empty thing == not accepting anything! I think you are aware of "empty language", which means "no string", So to rephrase, "accepts empty string" == "accepts no string" == "does not accepts anything". If you still have problems, please comment.
                      – lU5er
                      Mar 17 '17 at 12:17




                      @JB-Franco Acceptance of empty thing == not accepting anything! I think you are aware of "empty language", which means "no string", So to rephrase, "accepts empty string" == "accepts no string" == "does not accepts anything". If you still have problems, please comment.
                      – lU5er
                      Mar 17 '17 at 12:17












                      Thanks! - The fact you have explained in the above about DFA accepting empty string, can be related to what I have asked here: Why in a DFA the empty string distinguishes any accept state from any reject state?
                      – JB-Franco
                      Mar 17 '17 at 19:41






                      Thanks! - The fact you have explained in the above about DFA accepting empty string, can be related to what I have asked here: Why in a DFA the empty string distinguishes any accept state from any reject state?
                      – JB-Franco
                      Mar 17 '17 at 19:41






                      1




                      1




                      This answer is wrong because "accepts empty string" and "accepts no string" are not the same! The NFA with only one state and no transitions accepts no strings if the state is non-accepting, and the empty string (but no other strings) if the state is accepting. Similarly, a DFA can accept only the empty string and no others by having a start state which is accepting and then all transitions point to a non-accepting trap state like the one in this answer.
                      – Benjamin Cosman
                      May 29 '17 at 16:13






                      This answer is wrong because "accepts empty string" and "accepts no string" are not the same! The NFA with only one state and no transitions accepts no strings if the state is non-accepting, and the empty string (but no other strings) if the state is accepting. Similarly, a DFA can accept only the empty string and no others by having a start state which is accepting and then all transitions point to a non-accepting trap state like the one in this answer.
                      – Benjamin Cosman
                      May 29 '17 at 16:13














                      @BenjaminCosman, answer me one thing, what do you mean by empty string?
                      – lU5er
                      May 30 '17 at 17:25




                      @BenjaminCosman, answer me one thing, what do you mean by empty string?
                      – lU5er
                      May 30 '17 at 17:25


















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