Update peps/pep-0800.rst

Author: JelleZijlstra

peps/pep-0800.rst

@@ -246,7 +246,7 @@ a single solid base, that is the class's solid base. If there are multiple candi
 that class is the solid base. If no such candidate exists, the class does not have a valid solid base, and therefore cannot exist.
 
 Type checkers must check for a valid solid base when checking class definitions, and emit a diagnostic if they encounter a class
-definition that lacks a valid solid base. Type checkers must also use the solid base mechanism to determine whether types are disjoint,
+definition that lacks a valid solid base. Type checkers may also use the solid base mechanism to determine whether types are disjoint,
 for example when checking whether a type narrowing construct like ``isinstance()`` results in an unreachable branch.
 
 Example::