(v1, v2)
Returns the "common" part of the two values, for whatever "common"
        means for this class. For example, a string implementation would return
        the common shared prefix, for an int implementation it would return
        the minimum of the two numbers.

        If there is no common part, this method should return None.
Returns the "common" part of the two values, for whatever "common"
        means for this class. For example, a string implementation would return
        the common shared prefix, for an int implementation it would return
        the minimum of the two numbers.
Returns the common part of the two values for whatever common means for this class . For example a string implementation would return the common shared prefix for an int implementation it would return the minimum of the two numbers .
def common(v1, v2):
        """Returns the "common" part of the two values, for whatever "common"
        means for this class. For example, a string implementation would return
        the common shared prefix, for an int implementation it would return
        the minimum of the two numbers.

        If there is no common part, this method should return None.
        """

        raise NotImplementedError
def common ( v1 , v2 ) : raise NotImplementedError