theorem Th1:
  <*<*d*>*> is tabular
proof
  take n = 1;
  let x;
  assume
A1: x in rng <*<*d*>*>;
A2: len <*d*> = n by FINSEQ_1:39;
  rng <*<*d*>*> = {<*d*>} by FINSEQ_1:38;
  then x = <*d*> by A1,TARSKI:def 1;
  hence thesis by A2;
end;
