  In a couple of articles (Ford G W and O'Connell R F 1996 Nature 380 113 and
2002 J. Phys. A: Math. Gen. 35 4183) it was argued that the standard result for
the derivative of the hyperbolic cotangent in the literature, d \coth y/dy =
-{csch}^2 y is incomplete and the correct expression should have an additional
term proportional to the Dirac delta function. The purpose of this paper is to
demonstrate that this claim is incorrect.
