Like- and unlike-sign (left) and the like-sign-subtracted (right) invariant massdistribution of ${\rm K^0_S K} \pi$ triplets in $|y|< 0.5$ in minimum-bias pp collisions at $\s$ = 13 TeV. The subtracted distribution is fitted with the function defined by Eq. 1, and the dotted blue line describes the residual background distribution, which is given by Eq. 2.