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Proof of lemma in Narboux.svg en My illustration of lemma from ustrasbg fr html as described in Julien Narboux Mechanical Theorem Proving in Tarski Geometry Botana and Recio Eds ADG LNAI pp and based on Schwabhuser Szmielew and Tarski Metamathematische Methoden in der Geometrie ISBN In use at org php title Midpoint own