For example, in the classification of discontinuities:

This article describes the classification of discontinuities in the simplest case of functions of a single real variable taking real values.

Lehigh University, Bethlehem, Pennsylvania, U.S.A. "Classification of discontinuities of real functions".

A problem arises with inclusion of the cosmological constant in the standard model: i.e., the appearance of solutions with regions of discontinuities (see classification of discontinuities at typical matter density).