Section Primitive.
Variables (aT : finGroupType) (sT : finType).
Variables (G : {group aT}) (to : {action aT &-> sT}) (S : {set sT}).

Lemma trans_prim_astab x :
x \in S -> [transitive G, on S | to] ->
[primitive G, on S | to] = maximal_eq 'C_G[x | to] G.