Notation "''Sym_' T" := (Sym (Phant T))
(at level 8, T at level 2, format "''Sym_' T") : group_scope.
Notation "''Sym_' T" := (Sym_group (Phant T)) : Group_scope.
Notation "''Alt_' T" := (Alt (Phant T))
(at level 8, T at level 2, format "''Alt_' T") : group_scope.
Notation "''Alt_' T" := (Alt_group (Phant T)) : Group_scope.

Lemma trivial_Alt_2 (T : finType) : #|T| <= 2 -> 'Alt_T = 1.