'Substituion on the Dyadic.
Examples
>>> from sympy.physics.vector import ReferenceFrame
>>> from sympy import Symbol
>>> N = ReferenceFrame(\'N\')
>>> s = Symbol(\'s\')
>>> a = s * (N.x|N.x)
>>> a.subs({s: 2})
2*(N.x|N.x)'

def subs(self, *args, **kwargs):

    return sum([Dyadic([(v[0].subs(*args, **kwargs), v[1], v[2])]) for v in self.args], Dyadic(0))
