+;;; Return a System-Area-Pointer pointing to the data for the vector
+;;; X, which must be simple.
+;;;
+;;; FIXME: So it should be SIMPLE-VECTOR-SAP, right? (or UNHAIRY-VECTOR-SAP,
+;;; if the meaning is (SIMPLE-ARRAY * 1) instead of SIMPLE-VECTOR)
+;;; (or maybe SIMPLE-VECTOR-DATA-SAP or UNHAIRY-VECTOR-DATA-SAP?)