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 Th39:
  H is disjunctive implies (F = the_left_argument_of H iff ex G st
  F 'or' G = H) & (F = the_right_argument_of H iff ex G st G 'or' F = H)
proof
  assume
A1: H is disjunctive;
  then ex F,G st H = F 'or' G;
  then H.1 = 2 by FINSEQ_1:41;
  then not H is conjunctive by Th21;
  hence thesis by A1,Def31,Def32;
end;
