'Register the transformation used to switch to another coordinate system.
Parameters
to_sys
another instance of ``CoordSystem``
from_coords
list of symbols in terms of which ``to_exprs`` is given
to_exprs
list of the expressions of the new coordinate tuple
inverse
try to deduce and register the inverse transformation
fill_in_gaps
try to deduce other transformation that are made
possible by composing the present transformation with other already
registered transformation'

def connect_to(self, to_sys, from_coords, to_exprs, inverse=True, fill_in_gaps=False):

    (from_coords, to_exprs) = dummyfy(from_coords, to_exprs)
    self.transforms[to_sys] = (Matrix(from_coords), Matrix(to_exprs))
    if inverse:
        to_sys.transforms[self] = self._inv_transf(from_coords, to_exprs)
    if fill_in_gaps:
        self._fill_gaps_in_transformations()
