+;;; ANSI requires that SUBTYPEP relationships among built-in primitive
+;;; types never be uncertain, i.e. never return NIL as second value.
+;;; Prior to about sbcl-0.7.2.6, ATOM caused a lot of problems here
+;;; (because it's a negation type, implemented as a HAIRY-TYPE, and
+;;; CMU CL's HAIRY-TYPE logic punted a lot).
+(assert-t-t (subtypep 'integer 'atom))
+(assert-t-t (subtypep 'function 'atom))
+(assert-nil-t (subtypep 'list 'atom))
+(assert-nil-t (subtypep 'atom 'integer))
+(assert-nil-t (subtypep 'atom 'function))
+(assert-nil-t (subtypep 'atom 'list))
+;;; ATOM is equivalent to (NOT CONS):
+(assert-t-t (subtypep 'integer '(not cons)))
+(assert-nil-t (subtypep 'list '(not cons)))
+(assert-nil-t (subtypep '(not cons) 'integer))
+(assert-nil-t (subtypep '(not cons) 'list))
+;;; And we'd better check that all the named types are right. (We also
+;;; do some more tests on ATOM here, since once CSR experimented with
+;;; making it a named type.)
+(assert-t-t (subtypep 'nil 'nil))
+(assert-t-t (subtypep 'nil 'atom))
+(assert-t-t (subtypep 'nil 't))
+(assert-nil-t (subtypep 'atom 'nil))
+(assert-t-t (subtypep 'atom 'atom))
+(assert-t-t (subtypep 'atom 't))
+(assert-nil-t (subtypep 't 'nil))
+(assert-nil-t (subtypep 't 'atom))
+(assert-t-t (subtypep 't 't))
+;;; Also, LIST is now somewhat special, in that (NOT LIST) should be
+;;; recognized as a subtype of ATOM:
+(assert-t-t (subtypep '(not list) 'atom))
+(assert-nil-t (subtypep 'atom '(not list)))
+;;; These used to fail, because when the two arguments to subtypep are
+;;; of different specifier-type types (e.g. HAIRY and UNION), there
+;;; are two applicable type methods -- in this case