'Return the sum of the two operands.
>>> ExtendedContext.subtract(Decimal(\'1.3\'), Decimal(\'1.07\'))
Decimal("0.23")
>>> ExtendedContext.subtract(Decimal(\'1.3\'), Decimal(\'1.30\'))
Decimal("0.00")
>>> ExtendedContext.subtract(Decimal(\'1.3\'), Decimal(\'2.07\'))
Decimal("-0.77")'

def subtract(self, a, b):

    return a.__sub__(b, context=self)
