Delayed Derivative Operator

*To*: mathgroup at smc.vnet.net*Subject*: [mg81762] Delayed Derivative Operator*From*: ToddSmith <elliptic1 at gmail.com>*Date*: Wed, 3 Oct 2007 02:26:48 -0400 (EDT)

Hi, I would like to be able to have an equation eq := D[f[x],x]==5; And a substitution rule rule = f[x]->x^3; And perform the substitution eq/.rule And get back the equation 3x^2==5. But Mathematica sees f'[x] and doesn't do any substitutions. I tried a delayed assignment for eq but it didn't work. What can I do? -Thanks

**Follow-Ups**:**Re: Delayed Derivative Operator***From:*Curtis Osterhoudt <cfo@lanl.gov>

**Re: Delayed Derivative Operator***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>