Past exam of the mathematics course of the University of Cambridge / 2021 / iii / Paper 221 / 3 / a / Solution

A distribution is faithful to a Directed acyclic graph $G$ when every conditional independence in the distribution is implied by D-separation in $G$. Together with the graphical Markov property, faithfulness makes conditional independence equivalent to D-separation and rules out independences caused only by exact parameter cancellation.