Decidable Languages

1
Section 4.1
Decidable Languages

• Problems about regular languages
• - ADFA ltB,wgt B is a DFA that accepts string
  w
• ANFA ltB,wgt B is an NFA that accepts string
  w
• AREX ltR,wgt R is a reg.expr. that generates
  string w

2
Section 4.1
Decidable Languages
Problems about regular languages - EDFA ltAgt
A is a DFA, L(A) - EQDFA ltA,Bgt
A,B are DFAs, L(A) L(B)
3
Section 4.1
Decidable Languages
Problems about context-free languages - ACFG
ltG,wgt G is a CFG that accepts string w
4
Section 4.1
Decidable Languages
Problems about context-free languages - ECFG
ltGgt G is a CFG, L(G)
5
Section 4.1
Decidable Languages
Problems about context-free languages - EQCFG
ltG,Hgt G,H are CFGs, L(G) L(H)
???
6
Section 4.1
Decidable Languages
Problems about context-free languages Thm 4.9
Every CFL is decidable.