reserve p,q,r for FinSequence;
reserve u,v,x,y,y1,y2,z for object, A,D,X,Y for set;
reserve i,j,k,l,m,n for Nat;

theorem Th48:
  idseq(n + k) | Seg n = idseq n
proof
A1: Sgm(Seg n) = idseq n by Th46;
  Sgm(Seg(n + k)) = idseq(n + k) by Th46;
  hence thesis by A1,Lm4;
end;
