“…The arguments η i of this d log-form, which contain all the dependence of the DEQ on the kinematics, are referred to as the alphabet and they consist in the following 9 letters: Let us observe that, currently, there is neither a proof of existence, nor any systematic algorithm to build a basis of integrals whose system of DEQs is linear in . Nevertheless, by trial and error, we have been always able to find it within the physical contexts we have so far studied [41][42][43][44], as well as for the µe scattering. We believe it is a very important property which could be considered a prerequisite for the existence a canonical basis: in fact, a system of DEQs whose matrix is linear in can be brought into canonical form by a rotation matrix built either by means of Magnus exponential, or equivalently by means of the Wronskian matrix (formed by the solutions of the associated homogenous equations, and their derivatives), as shown for the case of systems of DEQs involving elliptic solutions [59][60][61].…”