src/Number.php
public function subtract(Number $subtractor)
    {
        $resultDecimalValue = $this->decimalValue() - $subtractor->decimalValue();

        $result = new Number($resultDecimalValue);

        return $result->convert($this->getNumberSystem());
    }
public function subtract(Number $subtractor)
    {
        $resultDecimalValue = $this->decimalValue() - $subtractor->decimalValue();

        $result = new Number($resultDecimalValue);

        return $result->convert($this->getNumberSystem());
    }
Subtract two numbers.
The number-system of the result will be the one of the number
who's was the called object.

@param Number $subtractor

@return Number