On The Ambiguity Problem of Backus Systems

Backus 1 has developed an elegant method of defining well-formed formulas for computer languages such as ALGOL. It consists of (our notation is slightly different from that of Backus): A finite alphabet: a 1 , a 2 , …, a t ; Predicates: P 1 , P 2 , …, P ϵ ; Productions, either of the form (a) a j ∈ P i ;