Suppose I have a function like
$\qquad f=\sinh(\eta)^2\times \sin(\theta)^2\times \cos(\phi)^2-\cosh(\eta)^2\times \sin(\theta)^2\times \sin(\phi)^2+\cdots$
I want to replace $\sinh(\eta)\times \sin(\theta)\times \cos(\phi)$ by $u_1$
I have tried with
Replace[f, Sinh[η] Sin[θ] Cos[ϕ] -> u1]
but unfortunately it's not working. I have come to know from the Mathematica Documentation Center that
Replace does not map down to subparts.
Would anyone be able to help me regarding this issue?