In a letter to Nature (Ford G W and O'Connell R F 1996 Nature 380 113) we presented a formula for the derivative of the hyperbolic cotangent that differs from the standard one in the literature by an additional term proportional to the Dirac delta function. Since our letter was necessarily brief, shortly after its appearance we prepared a more extensive unpublished note giving a detailed explanation of our argument. Since this note has been referenced in a recent article (Estrada R and Fulling S A 2002 J. Phys. A: Math. Gen. 35 3079) we think it appropriate that it now appear in print. We have made no alteration to the original note. [References: 2]
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机译：在给自然界的一封信中（Ford G W和O'Connell R F 1996 Nature 380 113），我们提出了双曲余切导数的公式，该公式与文献中的标准相差一个与狄拉克δ函数成比例的附加术语。由于我们的来信一定很简短，因此在其出现后不久，我们准备了更广泛的未发表的说明，对我们的论点进行了详细说明。由于最近的文章（Estrada R和Fulling S A 2002 J. Phys。A：Math。Gen. 35 3079）中已经引用了此注释，因此我们认为现在将其显示在印刷本中是适当的。我们没有对原始注释进行任何更改。 [参考：2]
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