  A recent paper [F. Radicchi and A. Arenas, Nature Phys. 9, 717 (2013)]
presented the finding of an abrupt transition in the structure of
interconnected networks. This transition was said to be generic and to occur
even in networks of finite size. Furthermore, it was remarked that this
singular behaviour could be understood in the spirit of a first-order phase
transition. We show here that the generic singularity found in that paper is a
trivial consequence of the reducibility of the "supra-Laplacian" operator
studied. The singular changes observed are therefore not related to any
collective abrupt structural transformation in the interconnected networks.
