End Primitive.
Section NactionDef.
Variables (gT : finGroupType) (sT : finType).
Variables (to : {action gT &-> sT}) (n :  nat).
Definition n_act (t : n.-tuple sT) a := [tuple of map (to^~ a) t].
Fact n_act_is_action : is_action setT n_act.
Canonical n_act_action := Action n_act_is_action.
End NactionDef.
Notation "to * n" := (n_act_action to n) : action_scope.
Section NTransitive.
Variables (gT : finGroupType) (sT : finType).
Variables (n :  nat) (A : {set gT}) (S : {set sT}) (to : {action gT &-> sT}).
Definition dtuple_on := [set t : n.-tuple sT | uniq t & t \subset S].
Definition ntransitive := [transitive A, on dtuple_on | to * n].

Lemma n_act_dtuple t a :
a \in 'N(S | to) -> t \in dtuple_on -> n_act to t a \in dtuple_on.