2013/11/12 by Michał R. Przybyłek, Michal R. Przybylek, Przybylek, Michal R.
Computer Science · Engineering · Mathematics · #Computability, Logic, AI Algorithms #Rings, Modules, and Algebras #graph theory and CDMA systems #math.CT
paper · pdf · doi:10.48550/arxiv.1311.2974
arxiv created 2014/10/05 · arxiv updated 2014/10/07
Given a composition of two commutative squares, one well-known pullback lemma says that if both squares are pullbacks, then their composition is also a pullback; another well-known pullback lemma says that if the composed square is a pullback and the supporting square is a pullback, then the other square is a pullback as well. This note investigates the third of the possibilities.