Regular Tur\'an numbers and some Gan-Loh-Sudakov-type problems

Motivated by a Gan-Loh-Sudakov-type problem, we introduce the regular Tur'an numbers, a natural variation on the classical Tur'an numbers for which the host graph is required to be regular. Among other results, we prove a striking supersaturation version of Mantel’s theorem in the case of a regular host graph of odd order. We also characterise the graphs for which the regular Tur'an numbers behave classically or otherwise.