Operate

gives

applies p at level n in the head of expr.

Operate is essentially a generalization of Apply, which allows you to apply an operator to the head of an expression, rather than simply to replace the head. »

Operate on the head of the expression with

Use a pure function:

Operate on the head of the expression with

Out[1]=

Use a pure function:

Out[1]=

Operate at level 1, the head of the expression (default):

Operate at level 2 (the head of the head of the expression):

Operate can be iterated:

Apply is a special case of Operate that replaces the head of the expression:

Operate followed by Through is a form of composition: