I like to think of these holes as having a begining point and an end point. In a torus, we can see the the object has one hole. What people do not realize is that there is in fact a beginning and an end to that hole. The begining of the hole is at the first half of the object. The ending is the other half. If you drill a hole into a straw, you can see that the holes sides are not perfectly flat. There is still some "straw" left on the sides with two corner areas on the inside and out side. Think of it as "a hole that intersects with another hole."
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