number types

*To*: mathgroup at smc.vnet.net*Subject*: [mg21613] number types*From*: Naum Phleger <naum at cava.physics.ucsb.edu>*Date*: Tue, 18 Jan 2000 02:35:06 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

I feel sort of silly asking something that should be so clear but after LOTS of trying I can't seem to get it right. How can I make Mathematica know that a variable is real or positive so that Conjugate[a] gives a Sqrt[ a^2 ] gives a when I evaluate integrals with a in them it doesn't give me an If statement like If[ Im[a]=0, answer I want , unevaluated integral ] this seems like it should be easy but I nothing that I try ever works. Thanks for any help.