Grammar re;
Lexer
        a = 'a';
        ab = 'ab';
        a_ab = a | ab;
        //alb_ab = 'a' Lookahead Not 'b' | 'ab';
        s = Shortest(a_ab);
        l = Longest(a_ab);
        dummy = 'x' (a|ab|s|l);
	blank = #10 | #13 | #32; 

Parser
Ignored blank;
	p = t+;
        t = 
        l | //alt1
//alt1        a | s |
//alt2        a |
        dummy;