Academic Editor: A. Yoshioka
Copyright © 2010 K. Uchino. This is an open access article distributed under the
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We will explain Arnold's 2-dimensional (shortly, 2D) projective geometry (Arnold, 2005) by means of lattice theory. It will be shown that the projection of the set of nontrivial triangular -matrices is the pencil of tangent lines of a quadratic curve on Arnold's projective plane.