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;
reserve sq,sq9 for FinSequence;

theorem
  H is conjunctive implies (F = the_left_argument_of H iff ex G st F '&'
G = H) & (F = the_right_argument_of H iff ex G st G '&' F = H) by Def31,Def32;
