theorem Th33:
  <*x,y*> is DTree-yielding iff x is DecoratedTree & y is DecoratedTree
proof
A1: x is DecoratedTree & y is DecoratedTree iff {x,y} is constituted-DTrees
  by Th17;
  rng <*x,y*> = {x,y} by FINSEQ_2:127;
  hence thesis by A1;
end;
