The Bolzano-Weierstrass method Divide the desert by a line running from north to south. The lion is then either in the eastern or in the western part. Lets assume it is in the eastern part. Divide this part by a line running from east to west. The lion is either in the northern or in the southern part.
Lets assume it is in the northern part.
We can continue this process arbitrarily and thereby constructing with each step an increasingly narrow fence around the selected area. The diameter of the chosen partitions converges to zero so that the lion is caged into a fence of arbitrarily small diameter. The set theoretical method We observe that the desert is a separable space. It therefore contains an enumerable dense set of points which constitutes a sequence with the lion as its limit. We silently approach the lion in this sequence, carrying the proper equipment with us.