shadow wiki:
>This article is about the optical phenomenon; for other meanings, see Shadow (disambiguation). A shadow is a region of darkness where light is blocked. A shadow occupies all the space behind an opaque object with light in front of it. The cross-section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the light.
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surface wiki:
>For other senses of this word, see surface (disambiguation). In mathematics (topology), a surface is a two-dimensional manifold. Examples arise in three-dimensional space as the boundaries of three-dimensional solid objects. The surface of a fluid object, such as a rain drop or soap bubble, is an idealisation. To speak of the surface of a snowflake, which has a great deal of fine structure, is to go beyond the simple mathematical definition. For the nature of real surfaces see surface tension, surface chemistry, surface energy, roughness.
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