theorem Th5: :: see SCMFSA_2:99
  Exec((f, aa) := bb, s).f = s.f+*(|.s.aa.|, s.bb)
proof
  ex k being Nat st k=|.s.aa.| & Exec((f,aa):=bb, s).f = s.f+*
  (k,s.bb) by SCMFSA_2:73;
  hence thesis;
end;
