reserve
  a for natural Number,
  k,l,m,n,k1,b,c,i for Nat,
  x,y,z,y1,y2 for object,
  X,Y for set,
  f,g for Function;
reserve p,q,r,s,t for FinSequence;
reserve D for set;

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;
