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 Th3:
  Seg 5 = {1,2,3,4,5}
proof
  thus Seg 5 = {1,2,3,4} \/ {4 + 1} by Th2,FINSEQ_1:9
    .= {1,2,3,4,5} by ENUMSET1:10;
end;
