> In 4d you can tie a sphere in a knot. Arguably you can do that in 3D, if you accept the horned sphere as a knot. Though I suppose that does raise the questio

> In 4d you can tie a sphere in a knot. Arguably you can do that in 3D, if you accept the horned sphere as a knot. Though I suppose that does raise the question of what you are willing to call a sphere. Regardless it's an embedding of a sphere that cannot be deformed into a unit sphere so I think the analogy holds.