Comments on “Translation-invariant bipolarons and the problem of high-temperature superconductivity”

We comment on the recent results of Refs. [1,2] on the bipolaron problem derived using an approximation of Gross–Tulub. It is proved that, contrary to the claim made in Refs. [1,2], the bipolaron ground-state energy calculated there in the strong-coupling approximation has not been shown to constitute a variational upper bound.