@arthur-adjedj was very confused when a mutually recursive definition
didn't work as expected, and the reason was that he used different names
for the fixed parameters.
It seems plausible to simply allow that and calculate the fixed-prefix
up to alpha renaming.
It does mean, though, that, for example, termination proof goals will
mention the names as used by the first function. But probably better
than simply failing. And we could even fix that later (by passing down
the
actual names, and renmaing the variables in the context of the mvar,
depending on the “current function”) should it bother our users.
78146190e5