We write $cl$ for the commutator length, i.e. the least number of commutators which multiply to a given element of a group.
Given an element $g$ in the commutator subgroup of the free group $G=F_2$ on two generators, is it true that $$cl_G(g) = \displaystyle \max_{\mbox{H < G finite index normal}} cl_H cl_{G/H} (g \mod H)$$ ?

