// input symbols
%{ a,b,1 1a %}

// expression declarations
%[
  $1=[&|(a|a b)(a b)*]
  $2=[a|(a|a a)(b a)* b]
  $3=[$1] - [$2]
%]

// evaluations

  $1 =? $2
  $1 = $3
  () in? $1
  $2 in? $1