(x-y) DiracDelta[x-y] does not simplify to 0

*To*: mathgroup at smc.vnet.net*Subject*: [mg56198] (x-y) DiracDelta[x-y] does not simplify to 0*From*: Alain Cochard <alain at geophysik.uni-muenchen.de>*Date*: Tue, 19 Apr 2005 04:54:54 -0400 (EDT)*Reply-to*: alain at geophysik.uni-muenchen.de*Sender*: owner-wri-mathgroup at wolfram.com

Mathematica 4.0 for Linux Copyright 1988-1999 Wolfram Research, Inc. -- Motif graphics initialized -- Considering that In[1]:= FullSimplify[x DiracDelta[x]] Out[1]= 0 I was surprised about this one: In[2]:= FullSimplify[(x-y) DiracDelta[x-y]] Out[2]= (x - y) DiracDelta[x - y] whereas: In[3]:= FullSimplify[(x-y) DiracDelta[x-y]/.x-y->z] Out[3]= 0 Is it simply that mma is a little weak on Out[2], or does it have a good reason for not simplifying, i.e., am I missing something at the mathematics level? Thanks in advance, Alain

**Follow-Ups**:**Re: (x-y) DiracDelta[x-y] does not simplify to 0***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>

**Re: (x-y) DiracDelta[x-y] does not simplify to 0***From:*yehuda ben-shimol <bsyehuda@gmail.com>