Why D[x', x] isn't 0 ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg66094] Why D[x', x] isn't 0 ?*From*: "Vladimir" <vladimir347 at yahoo.com>*Date*: Sat, 29 Apr 2006 03:40:49 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Hello! D[x'', x'] => 0 (* okay *) D[x', x] => x'' (* unexpected despite being similar to above *) D[f[x'], x] => x'' f'[x'] (* unexpected as well *) Why the last 2 lines don't produce zeroes and how to make them do so (for any function f) because it's quite common in mechanics where velocity is treated as independent of position, etc. -- Vladimir

**Follow-Ups**:**Re: Why D[x', x] isn't 0 ?***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>