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^Digital Camera Disasters: Will Yours Get Fixed? One widespread camera problem gets out-of-warranty repairs, another gets a lawsuit. (Grace Aquino, PC World, Tuesday 21 February 2006); ^ Repair guide; ^ IXUS 40 aka SD300 Repair Guide; ^ E18 quick fix (CNet Digital cameras forum); ^ Action by Horwitz, Horwitz & Associates at the Wayback Machine (archived 23 January 2013); ^ Investigation by ...
In optics, chromatic aberration (CA), also called chromatic distortion, color aberration, color fringing, or purple fringing, is a failure of a lens to focus all colors to the same point. [ 1 ] [ 2 ] It is caused by dispersion : the refractive index of the lens elements varies with the wavelength of light .
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In graph-theoretic terms, the theorem states that for loopless planar graph, its chromatic number is ().. The intuitive statement of the four color theorem – "given any separation of a plane into contiguous regions, the regions can be colored using at most four colors so that no two adjacent regions have the same color" – needs to be interpreted appropriately to be correct.
In graph theory, the De Bruijn–Erdős theorem relates graph coloring of an infinite graph to the same problem on its finite subgraphs. It states that, when all finite subgraphs can be colored with c {\displaystyle c} colors, the same is true for the whole graph.
According to Jensen & Toft (1995), the problem was first formulated by Nelson in 1950, and first published by Gardner (1960). Hadwiger (1945) had earlier published a related result, showing that any cover of the plane by five congruent closed sets contains a unit distance in one of the sets, and he also mentioned the problem in a later paper (Hadwiger 1961).