Re: How to evaluate parts of an expression, but not other parts?

*To*: mathgroup at smc.vnet.net*Subject*: [mg122695] Re: How to evaluate parts of an expression, but not other parts?*From*: Silvia <wyelen at gmail.com>*Date*: Sun, 6 Nov 2011 05:56:28 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <j930l9$a3d$1@smc.vnet.net>*Reply-to*: comp.soft-sys.math.mathematica at googlegroups.com

maybe you can use a Rule list to replace a, b, c, d outside the HoldForm. e.g. HoldForm[(a + b) + (c + d)] /. {a -> Sin[Pi/4]}