Keywords: Proof of lemma l7 21 in Narboux.svg en My illustration of lemma l7_21 from http //dpt-info u-strasbg fr/~narboux/tarski html as described in Julien Narboux 2007 Mechanical Theorem Proving in Tarski ™s Geometry F Botana and T Recio Eds ADG 2006 LNAI 4869 pp 139 “156 and based on W Schwabhäuser W Szmielew and A Tarski 1983 Metamathematische Methoden in der Geometrie ISBN 0387129588 In use at http //wikiproofs org/w/index php title Midpoint 2011-07-03 own based on File Parallelogram svg by en User Limaner which was released into the Public Domain Kingdon cc-zero Uploaded with UploadWizard Parallelograms |