Breckner, Wolfgang W. “A Principle of Condensation of Singularities for Set-Valued Functions”. Anal. Numér. Théor. Approx. 12, no. 2 (August 1, 1983): 101–111. Accessed April 14, 2025. https://ictp.acad.ro/jnaat/journal/article/view/1983-vol12-no2-art1.