let S1, S2 be Element of CQC-Sub-WFF ; :: thesis: ( S1 `2 = S2 `2 implies (CQCSub_& S1,S2) `2 = S1 `2 )
assume A1: S1 `2 = S2 `2 ; :: thesis: (CQCSub_& S1,S2) `2 = S1 `2
then CQCSub_& S1,S2 = Sub_& S1,S2 by Def4;
then CQCSub_& S1,S2 = [((S1 `1 ) '&' (S2 `1 )),(S1 `2 )] by A1, SUBSTUT1:def 21;
hence (CQCSub_& S1,S2) `2 = S1 `2 by MCART_1:7; :: thesis: verum