theorem Th37:
  S1`2 = S2`2 & CQC_Sub(S1) is Element of CQC-WFF(A) & CQC_Sub(S2) is
  Element of CQC-WFF(A) implies CQC_Sub(Sub_&(S1,S2)) is Element of CQC-WFF(A)
proof
  assume
A1: S1`2 = S2`2 & CQC_Sub(S1) is Element of CQC-WFF(A) & CQC_Sub(S2) is
  Element of CQC-WFF(A);
  S1`2 = S2`2 implies CQC_Sub(Sub_&(S1,S2)) = (CQC_Sub(S1)) '&' (CQC_Sub(
  S2)) by Th31;
  hence thesis by A1,CQC_LANG:9;
end;
