Re: How is ambiguity defined?

> But sentential forms are sequences of terminal and nonterminal
> symbols. The expression ‘a’*; ‘b’* is not a sentential form and
> cannot appear as a step in a derivation, as that term is normally
> defined. 


A nice try, but if I were to channel Chomsky, he would say that 


   s: a*; b*.


is a rewriting of


  s -> a*
  s -> b*


which have two derivations for 𝜀


Steven