Section RestrictPerm.
Variables (T : finType) (S : {set T}).
Definition restr_perm := actperm (<[subxx 'N(S | 'P)]>).
Canonical restr_perm_morphism := [morphism of restr_perm].

Lemma triv_restr_perm p : p \notin 'N(S | 'P) -> restr_perm p = 1.