reserve V, C for set;
reserve A, B, D for Element of Fin PFuncs (V, C);
reserve s for Element of PFuncs (V,C);

theorem Th15:
  for a be set holds a in A^B implies ex b,c be set st b in A & c
  in B & a = b \/ c
proof
  let a be set;
  assume a in A^B;
  then ex s,t be Element of PFuncs (V,C) st a = s \/ t & s in A & t in B & s
  tolerates t;
  hence thesis;
end;
