assuming certain properties about variables

*To*: mathgroup at smc.vnet.net*Subject*: [mg111403] assuming certain properties about variables*From*: Benjamin Hell <hell at exoneon.de>*Date*: Sat, 31 Jul 2010 02:40:03 -0400 (EDT)

Hi, let's say I have defined the following function: f[x_?Positive] = x Now I want to evaluate f with a variable t: f[t] As mathematica knows nothing about t, the output is f[t] instead of t. How can I tell mathematica, that t should be a positive number so that Positive[t] evaluates true and then f[t] evaluates to t? Of course this is just an example, which should present what I would like to know. Thanks in advance.