Motivated by recent work of Skinner—Sangiovanni-Vincentelli, we present an alternative interpretation of diagonal classes on triple products of modular curves via a pullback construction.

In their pioneering works on the subject, Darmon—Rotger and Bertolini—Seveso—Venerucci proved a regulator formula (sometimes called p-adic explicit reciprocity law) relating diagonal classes to triple product p-adic L-functions.

We show that, following our interpretation, the proof of the regulator formula becomes simpler and allows to cover cases that were not dealt with in the aforementioned works. This is joint work in progress with Ting-Han Huang and Ananyo Kazi.