Function auto_bind_implicits 

pub fn auto_bind_implicits(
    ctx: &Context,
    ty: &Term,
    body: &Term,
    existing_implicit: usize,
) -> (Term, Term, usize)

Auto-bind free type variables as leading implicit parameters. A definition written id : A -> A := fun a : A => a mentions A as a FREE, unregistered, single-uppercase global — the type-variable convention. This pass generalizes each such variable: it prepends Π(A:Type) to the type and λ(A:Type) to the body (converting Global(A) to the bound Var(A)), and returns the new implicit count, so A becomes an inferred implicit argument. Definitions that already bind their parameters reference them as Vars, not free Globals, so they are untouched — this only rescues what was previously an unbound-variable error.