Performance
-----------
-* [The complexity of comparing variables for equivalence during type
- unification is reduced from O(n!) to O(n)[1.9tu]. This leads
+* [The time complexity of comparing variables for equivalence during type
+ unification is reduced from _O_(_n_!) to _O_(_n_)][1.9tu]. This leads
to major compilation time improvement in some scenarios.
* [`ToString` is specialized for `str`, giving it the same performance
as `to_owned`][1.9ts].