theorem Th56:
  X is finite implies ex n st X,Seg n are_equipotent
proof
  assume X is finite;
  then reconsider n = card X as Nat;
A1: X,n are_equipotent by CARD_1:def 2;
  take n;
  n,Seg n are_equipotent by Lm1;
  hence thesis by A1,WELLORD2:15;
end;
