“…Therefore, there is a constant search for generalizations of these methods, which, in turn, leads to the definition of a series of concepts and alternative procedures to attack these more complicated cases. Among these, we highlight: [5,6,7,8,9,10,11,12,13,14] in the 'symmetry side' and [15,16,17,18,19,20,21,22,23,24] in the 'Darbouxian side'.…”