The function $f() is defined, and here's how you're attempting to call it:

$f() { y }: This defines a function named $f that simply outputs the variable $y. However, since $y is not defined within the function's scope, it will likely be empty or undefined.

$f(4)(): This is a nested function call.

$f(4): This part of the call passes the argument 4 to the function $f. () at the end: This attempts to execute the output of $f(4).