I have a large symbolic expression containing many terms of the form, LaplaceTransform[u2[z], z, s], with various functions for the first argument. I wish to replace these terms by l[u2[z]], but

LaplaceTransform[u2[z], z, s] /. LaplaceTransform[u_, z, s] -> l[u]

returns unevaluated. On the other hand,

Hypergeometric1F1[u2[z], z, s] /. Hypergeometric1F1[u_, z, s] -> l[u]


Plus[u2[z], z, s] /. Plus[u_, z, s] -> l[u]

return l[u2[z]], as expected. What subtlety am I missing?


The issue here is that the replacement rule LHS evaluates:

LaplaceTransform[u_, z, s] -> l[u]

(* Out[1402]= u_/s -> l[u] *)

To address this one can just prevent this with HoldPattern

LaplaceTransform[u2[z], z, s] /. 
 HoldPattern[LaplaceTransform[u_, z, s]] -> l[u]

(* Out[1401]= l[u2[z]] *)

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