theorem Th23:
  for d being data-only PartState of S, k being Nat
  holds d tolerates Start-At(k,S)
proof
  let d be data-only PartState of S, k be Nat;
  dom d misses dom Start-At(k,S) by Th10,ZFMISC_1:50;
  hence thesis by PARTFUN1:56;
end;
