“…Different realizations of these relations exist: they depend both on the form of Hamiltonians (scalar, matrix, multidimensional) and on the order of differential operators Q ± (linear or higher order in derivatives). Independently on realization, intertwining relations (3), (4) with nonsingular operators Q ± lead to the isospectrality of Hamiltonians H 1,2 , but up to possible zero modes of Q ± (see [74] as example of model with singular superpotential). Correspondingly, the wave functions are obtained from each other (up to the constant multipliers):…”