Function chalk_recursive::fulfill::is_trivial_canonical_subst  
source ยท fn is_trivial_canonical_subst<I: Interner>(
    interner: I,
    subst: &Substitution<I>,
) -> boolfn is_trivial_canonical_subst<I: Interner>(
    interner: I,
    subst: &Substitution<I>,
) -> bool