Definition add_case_pptrofs t si :=
if Archi.ptr64 then Cop.add_case_pl t else Cop.add_case_pi t si.

Lemma Ptrofs_repr_Int64_unsigned_special:
Archi.ptr64=true -> forall i, Ptrofs.repr (Int64.unsigned (Int64.repr i)) = Ptrofs.repr i.