fun valid_date (d:int, m:string) = if (m="January" orelse
									   m="March" orelse
									   m="May" orelse
									   m="July" orelse
									   m="August" orelse
									   m="October" orelse
									   m="December") andalso
									  d <= 31 andalso
									  d >= 0 then
									   true
								   else if (m="April" orelse
											m="June" orelse
											m="September" orelse
											m="November") andalso
										   d <= 30 andalso
										   d >= 0 then
									   true
								   else if m="February" andalso
										   d <= 28 andalso
										   d >= 0
								   then
									   true
								   else false