reserve n,m for Nat,
  r,r1,r2,s,t for Real,
  x,y for set;

theorem
  for D be non empty set, f be FinSequence of PFuncs(D,REAL), G be
  Element of PFuncs(D,REAL) holds Sum(<*G*>^f) = G + Sum f
proof
  let D be non empty set, f be FinSequence of PFuncs(D,REAL), G be Element of
  PFuncs(D,REAL);
  thus Sum(<*G*>^f) = Sum <*G*> + Sum f by Th21
    .= G + Sum f by FINSOP_1:11;
end;
