  This is a comment to the paper, Limitations on the superposition principle:
superselection rules in non-relativistic quantum mechanics by C Cisneros et al
1998 Eur. J. Phys. 19 237. doi:10.1088/0143-0807/19/3/005. The proof that the
authors construct for the limitation on the superposition of state vectors
corresponding to different sectors of the Hilbert space, partitioned by a
superoperator has a flaw as outlined below.
