1

A white sphere in front of a black sphere. From Jeff Ross (1997), Semantics of Media (Dordrecht: Kluwer), p. 73. © Kluwer. With kind permission from Springer Science and Business Media.

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2

A black sphere in front of a white sphere. From Jeff Ross (1997), Semantics of Media (Dordrecht: Kluwer), p. 73. © Kluwer. With kind permission from Springer Science and Business Media.

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3

A black sphere to the left.

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4

A black sphere to the right.

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5

A black sphere to the left from above.

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6

A black sphere to the right from above.

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7

An impossible triangle. Image from Wikimedia:
http://commons.wikimedia.org/wiki/File:Pentriangle.svg

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