Specifying sign or domain of a variable

*To*: mathgroup at smc.vnet.net*Subject*: [mg31458] Specifying sign or domain of a variable*From*: akronimus at yahoo.de (Andre)*Date*: Wed, 7 Nov 2001 05:29:27 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Hi, I want to determine the sign of a complex expression by specifying only the sign or the domains of the basic variables that appear in the expression (but not inputting any particular values). Unfortunately I have not been able to specify a variable as e.g. belonging to the set of positive reals and then using this information for determining the sign of an expression involving the variable. Does anybody know how to define variables as belonging to a specific set or to a domain and how to use these defintions in evaluating expressions composed of the basic variables? Thanks a lot for your help. Andre