Function php_is_hole_injective 

pub fn php_is_hole_injective(mono: Mono, holes: usize) -> bool

Is a PHP monomial hole-injective — no two of its edges share a hole? Standard PHP forbids two pigeons in one hole but allows a pigeon in several holes, so the at-most-one clauses force the GF(2) pseudo-expectation to vanish exactly on hole-collision monomials — i.e. its support lies in the hole-injective monomials (partial functions hole→pigeon). This is looser than a partial matching (which also forbids pigeon repeats) and is the correct GF(2) support.