Geometric Realization of Some Triangle-Free Combinatorial Configurations 𝟐𝟐_𝟑

Figure 5

A combinatorial automorphism of 11#(4,2;3), that is additional to the rotational symmetries. It arises by “split-mirror” reflection. The images of the upright numerals, each reflected in the mirror of the same color, are shown in italics. In fact, the “reflected” configuration is (up to a rotation) the one that arises by using in the construction as described above, the orientation opposite the one used originally. The particular “split-mirror” reflection is chosen so as to coincide with the one in (A.13) of [1], under the correspondence of Figure 2.