Flaška, V.; Ježek, J.; Kepka, T.; Kortelainen, J. (2007). Transitive Closures of Binary Relations I(PDF). Prague: School of Mathematics - Physics Charles University. p. 1. Archived from the original(PDF) on 2013-11-02. பார்க்கப்பட்ட நாள் 2015-09-29. Lemma 1.1 (iv). Note that this source refers to asymmetric relations as "strictly antisymmetric".
Flaška, V.; Ježek, J.; Kepka, T.; Kortelainen, J. (2007). Transitive Closures of Binary Relations I(PDF). Prague: School of Mathematics - Physics Charles University. p. 1. Archived from the original(PDF) on 2013-11-02. பார்க்கப்பட்ட நாள் 2015-09-29. Lemma 1.1 (iv). Note that this source refers to asymmetric relations as "strictly antisymmetric".