I don't know of a specific place that states this exact problem, but this is an application of the Squeeze theorem which can be found in any calculus textbook.
You haven't provided your reasoning for why you would be curious about this, so I'm left to assume that it's because from our local observations the universe appears to be a simply connected 3-manifold. There are two main reasons this doesn't imply the universe is the 3-sphere:
1) The...