{"ast_node_type":"other","tokens":[{"end":97,"kind":"keyword","start":0,"text":"//!"}]}
//! none of the `p_i`. We write `usefulness(p_1 .. p_n, q)` for a function that returns a list of
//! p_n`, a pattern `q` is said to be *useful* if there is a value that is matched by `q` and by
//! such values. The aim of this file is to compute it efficiently.