result = new EqualExpression(first,second);
}
else if (isLess(op))
result = new LessExpression(first,second);
else if (isLessEqual(op))
result = new LessEqualExpression(first,second);
else if (isGreat(op))
result = new GreatExpression(first,second);
else if (isGreatEq(op))
result = new GreatEqualExpression(first,second);
return result;