Function inner_horns_fill_uniquely 

pub fn inner_horns_fill_uniquely(g: &FiniteGroup, n: usize, k: usize) -> bool

Does every compatible inner horn (0 < k < n) fill uniquely? Unique inner fillers are the signature of a 1-truncated nerve — the ∞-groupoid is exactly K(G,1) = BG, no genuine higher cells.