Product derivative on derivative

Question

this is a silly question, probably. How to product derivative on derivative in Mathematica. I mean for example how to achieve this result:

Just more explanation. I need this for solving task with operators. I have two operators, for example:

I need to have the product of L1 on L2. When this is an operators of function y:

Answer 1

Try this:

    L1[u_] := D[u, x, \[Theta]];
L2[u_] := D[u, {x, 3}];
L3[u_] := L1[L2[u]];
L3[y[x, \[Theta]]]

yielding

Have fun!