“…Up to our knowledge, the first works in which it was realized the connection between PHA (called commutator representation in these papers) and Painlevé equations were [32] and [33]. Initially, both subjects were linked with first-order SUSY QM [5,6,27]; later on, this relation was further explored for the higher-order case [8,9,[28][29][30][31][34][35][36][37].Let us remark that the need to avoid singularities in the new potential V k (x) and the requirement for the Hamiltonian H k to be Hermitian lead to some restrictions [8]: (i) first of all, the relevant transformation function has to be real, which implies that the associated factorization energy is also real; (ii) as a consequence, the spectrum of H k consists of two independent physical ladders, an infinite one departing from the ground state energy E 0 of H 0 , plus a finite one with k equidistant levels, all of which have to be placed below E 0 . Regarding PV equation, these two restrictions imply that non-singular real solutions w(z; a, b, c, d) can be obtained just for certain real parameters a, b, c, d.From the spectral design point of view, however, it would be important to overcome restriction (ii) so that some (or all) steps of the finite ladder could be placed above E 0 .…”