fun max(tree) =
	case tree of
		LEAF t => SOME t
		|NODE(n, p, d) => if n >= valOf(max(p)) andalso n >= valOf(max(d))
						  then SOME n
						  else if valOf(max(p)) > valOf(max(d))
						  	   then max(p)
						  	   else max(d)