I need to express the countable property over a specific subset defined by a certain predicate P. My first idea was to explicitly state that there exists a function f which is bijective between my subset and, let's say, the natural numbers. Is there another more general way to express that property in the standard library ?
Thank you in advance
If you are using a set that is isomorphic to the natural numbers why don't you just use the natural numbers?
There is no way to distinguish isomorphic sets and in HoTT (or cubical agda) isomorphic sets are equal. Hence asking for a set that is isomorphic to Nat is the same as asking for a number that is equal to 3.