Corrections to
Probabilistic programming interfaces for random graphs:
Markov categories, graphons, and nominal sets.
Proc. ACM Program. Lang. 8, POPL, Article 61 (2024).
N. Ackerman, C. Freer, Y. Kaddar, J. Karwowski, S. Moss,
D. Roy, S. Staton and H. Yang.

Section 4.1.2, as written, does not present a category: the reindexing
relation given there is not a congruence, so composition is not well
defined on equivalence classes, and equation (19) does not describe the
hom-sets. The proof of Theorem 25 relies on it, and is incomplete in its
current form. The category itself does exist, and we have corrected
constructions that establish the theorem.

Sections 3, 5 and 6 are unaffected.

A corrigendum will follow.

Last updated August 2026.