  You are a financial analyst. At the beginning of every week, you are able to
rank every pair of stochastic processes starting from that week up to the
horizon. Suppose that two processes are equal at the beginning of the week.
Your ranking procedure is time consistent if the ranking does not change
between this week and the next one. In this paper, we propose a minimalist
definition of Time Consistency (TC) between two (assessment) mappings. With
very few assumptions, we are able to prove an equivalence between Time
Consistency and a Nested Formula (NF) between the two mappings. Thus, in a
sense, two assessments are consistent if and only if one is factored into the
other. We review the literature and observe that the various definitions of TC
(or of NF) are special cases of ours, as they always include additional
assumptions. By stripping off these additional assumptions, we present an
overview of the literature where the contribution of each author is
enlightened.
