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 Th16:
  for F,G holds (F '&' G).1 = 3
proof
  let F,G;
  thus (F '&' G).1 = (<*3*>^(F^G)).1 by FINSEQ_1:32
    .= 3 by FINSEQ_1:41;
end;
