An LL grammar is a formal grammar that can be parsed by an LL parser, which parses the input from Left to right, and constructs a Leftmost derivation of the sentence (hence LL, compared with LR parser that constructs a rightmost derivation).
Q : Prove that every LL grammar is not ambigious.
Note : I know how to show that a grammar is ambigious ( i should find two production sequence that lead to 1 string ) but i don't know how to show some grammar is not ambigious !!!