A triangle, in the sense of Schubert [1], is an entity in the plane S2 consisting of
(a) an ordered triad of points (P1, P2, P3);
(b) an ordered triad of lines (l1, l2, l3) connected with the points Pi by the incidence relations Pi ⊂ lj (i ≠ j); and
(c) a three base-point net Φof conies with the Pi as base-points.