Warning: Undefined array key "visitor_referer_type" in /var/www/vhosts/wordinf.com/core/app/libraries/Core.php on line 98 Hans Reichenbach - The concept of congruence in...
The concept of congruence in Euclidean geometry is not exactly the same as that in non-Euclidean geometry. ..."Congruent" means in Euclidean geometry the same as "determining parallelism," a meaning which it does not have in non-Euclidean geometry.