'Returns the inverse of a ``FreeGroupElement`` element
Examples
>>> from sympy.combinatorics.free_groups import free_group
>>> f, x, y, z = free_group("x y z")
>>> x.inverse()
x**-1
>>> (x*y).inverse()
y**-1*x**-1'

def inverse(self):

    group = self.group
    r = tuple([(i, (- j)) for (i, j) in self.array_form[::(-1)]])
    return group.dtype(r)
