He did not abandon mathematics completely, however, lecturing on the paradoxes of set theory (Burali-Forti paradox, Cantor's paradox, and Russell's paradox) to a meeting of the Deutsche Mathematiker–Vereinigung in 1903, and attending the International Congress of Mathematicians at Heidelberg in 1904.
De tódolos xeitos non abandonou completamente as matemáticas, ensinando os paradoxos da teoría de conxuntos (paradoxo de Burali-Forti, paradoxo de Cantor, e paradoxo de Russell) nunha reunión da Sociedade Matemática Alemá en 1903, e asistindo ao Congreso Internacional de Matemáticos de 1904 en Heidelberg.