let X, Y be Subset of CQC-WFF ; :: thesis: (Cn X) \/ (Cn Y) c= Cn (X \/ Y)
( Cn X c= Cn (X \/ Y) & Cn Y c= Cn (X \/ Y) ) by CQC_THE1:39, XBOOLE_1:7;
hence (Cn X) \/ (Cn Y) c= Cn (X \/ Y) by XBOOLE_1:8; :: thesis: verum