Exercise 15:

{gCFG({a,b})L(g)={a,b}}{GL(G)={waa:w{a,b}}}\{g\in\mathtt{CFG}(\{a,b\})\mid\mathcal{L}(g)=\{a,b\}^*\}\quad\leq\quad\{G\mid\mathcal{L}(G)=\{waa : w\in\{a,b\}^*\}\}
Reduce the universality problem on CFGs over {a,b}\{a,b\} to the problem of whether a CFG generates all words over {a,b}\{a,b\} that end with aaaa, in order to prove that such problem is not semi-decidable (not recursively enumerable).
Authors: Carles Creus, Guillem Godoy / Documentation:
To be able to submit you need to either log in, register, or become a guest.