Subcountability (original) (raw)

In constructive mathematics, a collection is subcountable if there exists a partial surjection from the natural numbers onto it.This may be expressed as where denotes that is a surjective function from a onto . The surjection is a member of and here the subclass of is required to be a set.In other words, all elements of a subcountable collection are functionally in the image of an indexing set of counting numbers and thus the set can be understood as being dominated by the countable set .