stackless is now covariant

src/ch04/s00-concerns.md

@@ -1,21 +1,27 @@
 # Concerns (questions) with the current implementaion
 
 ## There exist alternative `Functor` implementations
+
 See the [relevant subchapter](./s01-alternatives.md)
 
 ## ~~It might be better to have a per-lifetime trait for `Functor`s~~ done
+
 See the [relevant subchapter](./s02-lifetimes.md)
 
 ## `Stackless` is kind of bad
+
 See the [relevant subchapter](./s03-stackless.md)
 
 ## `WeakFunctor<'a>` is not (yet) covariant over the lifetime `'a`
+
 See the [relevant subchapter](./s04-covariance.md)
 
 ## `Fail`/`FailMonad`/etc. have unclear semantics
+
 See the [relevant subchapter](./s05-fail.md)
 
 ## Is `FutureInstance` actually feasible?
+
 Todo: measure `futures::join` performance.
 
 ## Can `WeakFunctor` be an associated type of a `Functor` instead of its supertype?

src/ch04/s01-alternatives.md

@@ -44,6 +44,7 @@ fn fmap<'a, T: Functor<'a>, A: 'a + Clone, B: 'a + Clone>(
 ## `Clone`-`FnMut` category functors
 
 We view use of `FnMut` for category's morphisms as somewhat controversial[^e].
+
 * Use of direct/indirect mutable references is, arguably, counter-functional[^e].
 * `Clone+FnMut` is, generally, nonsensical[^e].
 * Due to that, morphisms category isn't a subcategory, so can't be wrapped.

src/ch04/s02-lifetimes.md

@@ -1,6 +1,7 @@
 # Making lifetimes a parameter of a trait instead of that of the GAT
 
 Current:
+
 ```rust
 pub trait WeakFunctorAny {
     type F<'a, A: 'a>: 'a

src/ch04/s03-stackless.md

@@ -1,4 +1,4 @@
-# `Stackless<'a>` isn't covariant
+# ~~`Stackless<'a>` isn't covariant~~ Fixed
 
 Current hypothesis is that this comes from `EvalTree<'a>` being invariant over `'a`
 due to `FnOnce` being invariant over its output,

src/ch04/s04-covariance.md

@@ -1,5 +1,5 @@
-**`CovariantFunctor` was deleted.**
+# **`CovariantFunctor` was deleted**
 
-## Specific case: `Stackless<'a>` isn't covariant
+## ~~Specific case: `Stackless<'a>` isn't covariant~~
 
-See the [relevant subchapter](s03-stackless.md)
+~~See the [relevant subchapter](s03-stackless.md)~~