Minimum transformation representations of diagram monoids

We obtain formulae for the minimum transformation degrees of the most well-studied families of finite diagram monoids, including the partition, Brauer, Temperley–Lieb and Motzkin monoids. For example, the partition monoid $P_n$ has degree $1+\frac{B(n+2)-B(n+1)+B(n)}{2}$ for $n\ge 2$, where these are Bell numbers. The proofs involve constructing explicit faithful representations of the minimum degree, many of which can be realised as (partial) actions on projections.