Still, there are some other inconsistencies between these two files
that may need fixing, like whether to take fork into account or not
and order of arguments.

These are no longer needed, since fill is no longer a type class.

Remarks:
* eauto needs more fuel to automatically solve the side-conditions.
* ssreflect rewrite works if we do a set (φ ..) first. No idea why.

...unfortunately, that proof actually got longer because some automation no longer works