type FilterOut<T extends any[], F> = T extends [infer E, ...infer Rest]
  ? [F] extends [E]
    ? FilterOut<Rest, F>
    : [E, ...FilterOut<Rest, F>]
  : [];

type FilterOut2<T extends any[], F> = T extends [infer E, ...infer Rest]
  ? [E] extends [F]
    ? FilterOut<Rest, F>
    : [E, ...FilterOut<Rest, F>]
  : [];

type Test = FilterOut<["a", never], never>;
//Output []

type Test2 = FilterOut2<["a", never], never>;
//Output ["a"]

It’s different Output

playground

I had lookup typescript’s document about conditional type , but not get the reason。

So, Why [E] extends [F] and [F] extends [E] do not have same effect in this case?