if (bin.op()==ExprOperator.PRODUCT && bin.left()==s) return bin.right();
}
return s.join(s2);
case EQUALS:
obj=visitThis(a);
if (obj instanceof IntExpression) { i=(IntExpression)obj; f=i.eq(cint(b));}
else { s=(Expression)obj; f=s.eq(cset(b)); }
return k2pos(f,x);
case NOT_EQUALS:
obj=visitThis(a);
if (obj instanceof IntExpression) { i=(IntExpression)obj; f=i.eq(cint(b)).not();}