α-isoptics of a triangle and their connection to α-isoptic of an oval
Rendiconti del Seminario Matematico della Università di Padova, Tome 133 (2015), pp. 159-172. 
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Michalska, Małgorzata; Mozgawa, Witold. $\alpha $-isoptics of a triangle and their connection to α-isoptic of an oval. Rendiconti del Seminario Matematico della Università di Padova, Tome 133 (2015), pp. 159-172. http://www.numdam.org/item/RSMUP_2015__133__159_0/

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