// input symbols %{ a,b,c,d %} // expression declarations %[ $1=[&|(a|a b)(a b)*] $2=[a|(a|a a)(b a)* b] $3=![$1] + [a (a b)*] $4=[$1] - [$2] $5=[$1] + [$2] $6=[$1] # [$2] $7=![[![$1]] # [![$2]]] $8=![[![$1]] + [![$2]]] %] // evaluations $1 =? $2 $2 in? $1 () in? $1 (a a b a b) in? $1 (a a a b a b) in? $1 $5 =? $7 $6 =? $8