“…The analysis of resonances [3,4,5,6,7,8] is transparent for rectangular potentials in either, the presence of a background interaction [9,10], or in free space [11,12,13,14,15,16,17]. Simple models of point-like [18,19], as well as regularized singular interactions [20], can be obtained as limit cases of rectangular potentials [21,17,22]. The one-dimensional models are also useful in the study of supersymmetric quantum mechanics [23,24,25,26,27].…”