Think of f as a function that takes a value and returns a value. Y takes a function and returns a function. Y(f) returns a new function that takes a value and applies f to it, recursively forever, ultimately converging on a value (or infinity).
In your example, f(...) would have to return a function that is then applied to x.
Comments
I think that should be (Y(f))(x) = f(f(f(...)))(x)
Think of f as a function that takes a value and returns a value. Y takes a function and returns a function. Y(f) returns a new function that takes a value and applies f to it, recursively forever, ultimately converging on a value (or infinity).
In your example, f(...) would have to return a function that is then applied to x.
I realize there are no non-function values in LC.