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 Th2:
  Seg 4 = {1,2,3,4}
proof
  thus Seg 4 = {1,2,3} \/ {3 + 1} by Th1,FINSEQ_1:9
    .= {1,2,3,4} by ENUMSET1:6;
end;
