theorem
  for p being PartState of S, k being Nat
  holds DataPart DecIC(p,k) = DataPart p
proof
  let p be PartState of S, k be Nat;
  thus DataPart DecIC(p,k)
  = DataPart p +* DataPart Start-At(IC p-'k,S) by FUNCT_4:71
    .= DataPart p +* {} by Th20
    .= DataPart p;
end;
