for A being QC-alphabet
for S1, S2 being Element of QC-Sub-WFF A st S1 `2 = S2 `2 & CQC_Sub S1 is Element of CQC-WFF A & CQC_Sub S2 is Element of CQC-WFF A holds
CQC_Sub (Sub_& (S1,S2)) is Element of CQC-WFF A