BooleanValue ret = lookup(compFormula);
if (ret!=null) return ret;
final BooleanMatrix left = compFormula.left().accept(this);
final BooleanMatrix right = compFormula.right().accept(this);
final ExprCompOperator op = compFormula.op();
switch(op) {
case SUBSET : ret = left.subset(right); break;
case EQUALS : ret = left.eq(right); break;
default :