Thank you, luisfe, for this detailed reply!
Of course it would be formally nice to have the map
lambda x: x.map_coefficients(phi)
be an actual sage homomorphism (which it will always be if phi is a
homomorphism of coefficient rings). But for now what you propose works
fine for me.
--
You rec
Within a specific interactive session, you could do the following, when
creating the rings:
sage: R = PowerSeriesRing(GF(2),'t')
sage: F = R.residue_field()
sage: phi = R.hom([0], F)
sage: F.register_coercion(phi)
This way, you are indicating that the morphism phi should be considered a
coercio
