APA (7th ed.) Citation

Leo <Papa, X., & Pius <Papa, X. Rerum novarum: Die Sozialen Enzykliken Leos XIII.und Pius XI. Tyrolia-Verlag.

Chicago Style (17th ed.) Citation

Leo <Papa, XIII.>, and XI.> Pius <Papa. Rerum Novarum: Die Sozialen Enzykliken Leos XIII.und Pius XI. Innsbruck [u.a.]: Tyrolia-Verlag.

MLA (8th ed.) Citation

Leo <Papa, XIII.>, and XI.> Pius <Papa. Rerum Novarum: Die Sozialen Enzykliken Leos XIII.und Pius XI. Tyrolia-Verlag.

Warning: These citations may not always be 100% accurate.