Definition group_of of phant gT : predArgType := group_type.
Local Notation groupT := (group_of (Phant gT)).
Identity Coercion type_of_group : group_of >-> group_type.
Canonical group_subType := Eval hnf in [subType for gval].
Definition group_eqMixin := Eval hnf in [eqMixin of group_type by <:].
Canonical group_eqType := Eval hnf in EqType group_type group_eqMixin.
Definition group_choiceMixin := [choiceMixin of group_type by <:].
Canonical group_choiceType :=
Eval hnf in ChoiceType group_type group_choiceMixin.
Definition group_countMixin := [countMixin of group_type by <:].
Canonical group_countType := Eval hnf in CountType group_type group_countMixin.
Canonical group_subCountType := Eval hnf in [subCountType of group_type].
Definition group_finMixin := [finMixin of group_type by <:].
Canonical group_finType := Eval hnf in FinType group_type group_finMixin.
Canonical group_subFinType := Eval hnf in [subFinType of group_type].
(* No predType or baseFinGroupType structures, as these would hide the *)
(* group-to-set coercion and thus spoil unification.                  *)
Canonical group_of_subType := Eval hnf in [subType of groupT].
Canonical group_of_eqType := Eval hnf in [eqType of groupT].
Canonical group_of_choiceType := Eval hnf in [choiceType of groupT].
Canonical group_of_countType := Eval hnf in [countType of groupT].
Canonical group_of_subCountType := Eval hnf in [subCountType of groupT].
Canonical group_of_finType := Eval hnf in [finType of groupT].
Canonical group_of_subFinType := Eval hnf in [subFinType of groupT].
Definition group (A : {set gT}) gA : groupT := @Group A gA.
Definition clone_group G :=
let: Group _ gP := G return {type of Group for G} -> groupT in fun k => k gP.

Lemma trivgP : reflect (G :=: 1) (G \subset [1]).