In this Act:
"supply authority"—each of the following is a supply authority :
(a) a written prescription;
(b) a written requisition;
(c) a purchase order;
(d) a standing order;
(e) a document that purports to be a document mentioned in paragraph (a), (b), (c) or (d).
Note A purchase order and standing order must be in writing (see the definitions of these terms in the dictionary).