/**
* Subtracts two numbers to return the difference. The second argument is
* subtracted from the first argument.
*
* The arguments can be any valid expression as long as they resolve to numbers and/or dates.
*
* @see http://docs.mongodb.org/manual/reference/operator/aggregation/subtract/
* @see Expr::subtract
* @param mixed|Expr $expression1
* @param mixed|Expr $expression2
* @return self
*/
public function subtract($expression1, $expression2)
{
$this->expr->subtract($expression1, $expression2);
return $this;
}