Neat inverting of log rule

*To*: mathgroup at yoda.physics.unc.edu*Subject*: Neat inverting of log rule*From*: rvs at amnesix.kfunigraz.ac.at (Reinhard V.Simonovits)*Date*: Mon, 14 Mar 1994 19:36:43 +0100

Dear MathGroupers! I am looking for a neat implementation of "inverse log rules"; I tried Off[General::spell1] log[a_ b_] = log[a] + log[b]; log[a_^n_] = n log[a]; expr = log[a b^2 c^3] log[a] + 2 log[b] + 3 log[c] ok, it works. The goal is to invert the rules, to get log[a b^2 c^3]. Apply[ f, expr, 2] f[a] + f[ 2, f[b]] + f[3, f[c]] exprtemp = Apply[f, expr, 2] //. { f[a_] + f[b_] -> f[a b], f[n_, f[a_] -> f[b^n] } f[a b^2 c^3] Apply[ HoldForm[log], exprtemp ] log[a b^2 c^3] Ok. I think, my changing of the label is anyway "unfair". Can anyone give me an advice how to obtain the same result using only the log label? This means to make log forget about its two first learned rules when inverting the expr. Reinhard Simonovits, Univ. Graz, Austria