reserve k,m,n for Element of NAT,
  a,X,Y for set,
  D,D1,D2 for non empty set;
reserve p,q for FinSequence of NAT;
reserve x,y,z,t for Variable;
reserve F,F1,G,G1,H,H1 for ZF-formula;

theorem Th21:
  H is conjunctive implies H.1 = 3
proof
  assume H is conjunctive;
  then consider F,G such that
A1: H = F '&' G;
  <*3*>^F^G = <*3*>^(F^G) by FINSEQ_1:32;
  hence thesis by A1,FINSEQ_1:41;
end;
