We prove that in a regular category all reflexive and transitive relations are symmetric if and only if every internal category is an internal groupoid. In particular, these conditions hold when the category is n-permutable for some n.
Martins-Ferreira, N., Rodelo, D., & Van der Linden, T. (2014). An observation on n-permutability. Belgian Mathematical Society - Simon Stevin. Bulletin, 21(2), 223-230. https://hdl.handle.net/2078.5/60569 (Original work published 2014)