Using Replace with

Question

I have an expression

    expr=Derivative[1][A][\[Zeta]] + Derivative[2][A][\[Zeta]] + 
 Derivative[3][A][\[Zeta]] + Derivative[4][A][\[Zeta]]

I want to replace with the following:

where n>=2

Answer 1

Try

expr /. {
Derivative[i_ /; i>=2&&EvenQ[i]][A][\[Zeta]] -> P [\[Zeta]], 
Derivative[i_ /; i>=2&&OddQ[i]][A][\[Zeta]] -> P' [\[Zeta]]}

$A'(\zeta )+P'(\zeta )+2 P(\zeta )$