Section IrrConstt.
Variable (gT : finGroupType) (G H : {group gT}).
Definition irr_constt (B : {set gT}) phi := [pred i | '[phi, 'chi_i]_B != 0].

Lemma cfun_sum_constt (phi : 'CF(G)) :
phi = \sum_(i in irr_constt phi) '[phi, 'chi_i] *: 'chi_i.