documentcloud/underscore — pull request #518 by joshdk (2012-03-22 21:27:15+00:00)
Title: Quantifiers, exactly and only

Currently, underscore implements two different quantifiers;

* The universal quantifier `∀` `_.all`, "do all elements pass a truth test?".
* The existential quantifier `∃` `_.any`, "do any elements pass a truth test?".

This for aims to add two more quantifiers;

* An exact quantifier `_.exactly`, "do exactly n elements pass a truth test?".
* The uniqueness quantifier `∃!` `_.only`, "does only one element pass a truth test?". This is a specific case of exactly, where n is 1.