reserve n for Nat,
  a, b, r, w for Real,
  x, y, z for Point of TOP-REAL n,
  e for Point of Euclid n;
reserve V for RealLinearSpace,
        p,q,x for Element of V;

theorem Th26:
  q in halfline(p,q)
proof
  (1-1)*p + 1 * q = 0 * p + q by RLVECT_1:def 8
    .= 0.V + q by RLVECT_1:10
    .= q by RLVECT_1:4;
  hence thesis;
end;
