%start G 

%%

G   : A12345678 B12345678 // Comment
      C12345678 B12345678 B123456780123456789
      A123456780123456789 B123456780123456789 B12345678 B123456780123456789 B12345678
    ;

A12345678
    : "a"
    ;

B12345678
    : "b"
    ;

C12345678
    : "c"
    ;

A123456780123456789
    : "ax"
    ;

B123456780123456789
    : "bx"
    ;