%% A context-free grammar for strings with an equal number of 0's and 1's in any order.
%% s -> 0 a | 1 b | lambda
%% a -> 1 | 1s | 0aa           This is the "You owe me a 1 rule"
%% b -> 0 | 0s | 1bb           This is the "You owe me a 0 rule"

variable(s).
variable(a).
variable(b).

terminal(0).
terminal(1).

rule(s, [0, a]).
rule(s, [1, b]).
rule(s, []).

rule(a, [1]).
rule(a, [1, s]).
rule(a, [0, a, a]).

rule(b, [0]).
rule(b, [0, s]).
rule(b, [1, b, b]).