reserve n,i,k,m for Nat;
reserve r,r1,r2,s,s1,s2 for Real;
reserve p,p1,p2,q1,q2 for Point of TOP-REAL n;

theorem Th11:
  p1 is_extremal_in LSeg(p1,p2) by RLTOPSP1:68,Th7;
