Converting a number back to a symbol?

*To*: mathgroup at smc.vnet.net*Subject*: [mg82881] Converting a number back to a symbol?*From*: AES <siegman at stanford.edu>*Date*: Fri, 2 Nov 2007 03:29:06 -0500 (EST)*Organization*: Stanford University

If we have an expression containing integer powers of the symbol u0 and we know that u0's numerical value is (or at least eventually will be) u0 = Pi/2, we know what happens if we write expr /. {u0 -> Pi/2} But what about the reverse case: we have an expression containing various integer powers of Pi, and we want to replace all the explicitly appearing Pi's by 2 u0. Writing expr /. {Pi-> 2 u0} doesn't seem to do it. Is there a way?