Problem with transformation rule of a function

*To*: mathgroup at smc.vnet.net*Subject*: [mg53467] Problem with transformation rule of a function*From*: Alain Cochard <alain at geophysik.uni-muenchen.de>*Date*: Thu, 13 Jan 2005 03:12:10 -0500 (EST)*References*: <16858.22033.555637.91757@localhost.localdomain>*Sender*: owner-wri-mathgroup at wolfram.com

I define an expression: In[1]:= expr=M[1][t] + M[2][t] + Integrate[M[1][t],t] + Integrate[M[2][t],t] + D[M[1][t],t] + D[M[2][t],t]; Out[1]= Integrate[M[1][t], t] + Integrate[M[2][t], t] + M[1][t] + M[2][t] + > (M[1])'[t] + (M[2])'[t] and then I try 2 transformation rules on this expression: In[2]:= vers1=expr/.{M[1][t]->f[t], M[2][t]->0} Out[2]= f[t] + Integrate[f[t], t] + (M[1])'[t] + (M[2])'[t] In this first one, I get the output I expect for the function and integration terms, but not for the derivative ones. In[3]:= vers2=expr/.{M[1]->f, M[2]->0} Out[3]= 0[t] + f[t] + Integrate[0[t], t] + Integrate[f[t], t] + f'[t] In this second version, I get these 0[t] terms for the function and integration terms, with which I further have to deal with to achieve what I want: In[4]:= %/.{0[t]->0} Out[4]= f[t] + Integrate[f[t], t] + f'[t] I would first like to understand why the derivation and integration terms are not treated in an identical way, and then I would like to know if there is a more elegant way to do what I want in a single step. Thanks in advance, AC

**Follow-Ups**:**Re: Problem with transformation rule of a function***From:*DrBob <drbob@bigfoot.com>