A seashell?

It seems the photo of a seashell, instead it’s a virtual image. Image used in the double...

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A trefoil knot

The trefoil knot is the simplest knot; here you can see the two versions (left and right) ...

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A trefoil knot

The trefoil knot is the simplest knot; here you can see the two versions (left and right) ...

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Road signs

Horizontal road signs: the image is very elongated, so that it can be seen rightly, as in ...

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