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 Th10:
  k + n in Seg k implies n = 0
proof
  assume k + n in Seg k;
  then k + n <= k + 0 by FINSEQ_1:1;
  hence thesis by XREAL_1:6;
end;
