In Response To 'Re: Factoring expression with diracdelta'
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oops - a typo...
the DiracDelta[y] on the right hand side of the rule should be a DiracDelta[w].
expr //. v_.*DiracDelta[w_] DiracDelta[x_] +
y_.*DiracDelta[w_] DiracDelta[x_] -> (v + y)*
DiracDelta[w] DiracDelta[x]