reserve i, n for Nat,
  x, y, a for Real,
  v for Element of n-tuples_on REAL,
  p, p1, p2, p3, q, q1, q2 for Point of TOP-REAL n;

theorem :: Triangle
  |.p+q.| <= |.p.| + |.q.|
proof
A1: len p = n & len q = n by CARD_1:def 7;
  thus thesis by A1,Th15;
end;
