+ ((eq type2 *extended-sequence-type*)
+ (typecase type1
+ (structure-classoid *empty-type*)
+ (classoid
+ (if (member type1 *non-instance-classoid-types* :key #'find-classoid)
+ *empty-type*
+ (if (find (classoid-layout (find-classoid 'sequence))
+ (layout-inherits (classoid-layout type1)))
+ type1
+ nil)))
+ (t
+ (if (or (type-might-contain-other-types-p type1)
+ (member-type-p type1))
+ nil
+ *empty-type*))))