-Any or all type declarations may be believed without runtime
-assertions, and assertions that are done may be imprecise.
+Declared types may be simplified into faster to check supertypes: for example,
+@code{(and unsigned-byte fixnum)} is simplified into @code{fixnum}.
+
+@strong{Note}: it is relatively easy to corrupt the heap when weak
+type checks are used if the program contains type-errors.