(* (c) Copyright 2006-2016 Microsoft Corporation and Inria.                  *)
(* Distributed under the terms of CeCILL-B.                                  *)
From mathcomp
From mathcomp
From mathcomp
(******************************************************************************)
(* n-transitive and primitive actions:                                        *)
(*  [primitive A, on S | to] <=>                                              *)
(*       A acts on S in a primitive manner, i.e., A is transitive on S and    *)
(*       A does not act on any nontrivial partition of S.                     *)
(*  imprimitivity_system A to S Q <=>                                         *)
(*       Q is a non-trivial primitivity system for the action of A on S via   *)
(*       to, i.e., Q is a non-trivial partiiton of S on which A acts.         *)
(*       to * n == in the %act scope, the total action induced by the total   *)
(*                 action to on n.-tuples. via n_act to n.                    *)
(*  n.-dtuple S == the set of n-tuples with distinct values in S.             *)
(*  [transitive^n A, on S | to] <=>                                           *)
(*       A is n-transitive on S, i.e., A is transitive on n.-dtuple S         *)
(*              == the set of n-tuples with distinct values in S.             *)
(******************************************************************************)
Set Implicit Arguments.
Unset Strict Implicit.
Unset Printing Implicit Defensive.
Section PrimitiveDef.
Variables (aT : finGroupType) (sT : finType).
Variables (A : {set aT}) (S : {set sT}) (to : {action aT &-> sT}).
Definition imprimitivity_system Q :=
[&& partition Q S, [acts A, on Q | to^*] & 1 < #|Q| < #|S|].
Definition primitive :=
[transitive A, on S | to] && ~~ [exists Q, imprimitivity_system Q].
End PrimitiveDef.
Arguments imprimitivity_system {aT sT} A%g S%g to%act Q%g.
Arguments primitive {aT sT} A%g S%g to%act.
Notation "[ 'primitive' A , 'on' S | to ]" := (primitive A S to)
(at level 0, format "[ 'primitive'  A ,  'on'  S  |  to ]") : form_scope.
Section Primitive.
Variables (aT : finGroupType) (sT : finType).
Variables (G : {group aT}) (to : {action aT &-> sT}) (S : {set sT}).

Lemma prim_trans_norm (H : {group aT}) :
[primitive G, on S | to] -> H <| G ->
H \subset 'C_G(S | to) \/ [transitive H, on S | to].