14) The alternating red-green path between r and g which isolates the first y region from b must exist by the same reasoning as for CASE 1. This means that the yellow and blue regions in the area containing the first y region can swap colors, turning that yellow region blue.
15) Likewise, the same argument can be used to show that there must exist a path of alternating blue-green regions from b to g which isolate the second y region from r. This means that the yellow and red regions in that region can swap colors, turning that y region red.
16) Because steps 14 and 15 allow us to recolor both y regions to other colors, we can arrive at a 4-coloring of M-v in which no neighbor of v is yellow. Therefore coloring v = yellow results in a 4-coloring of M. This proves that CASE 2 must also be false. Since both cases are false, M (which was any smallest counter-example) cannot exist proving that there can be no counter-examples, and that all finite planar maps must be 4-colorable.
14) The alternating red-green path between r and g which isolates the first y region from b must exist by the same reasoning as for CASE 1. This means that the yellow and blue regions in the area containing the first y region can swap colors, turning that yellow region blue.
15) Likewise, the same argument can be used to show that there must exist a path of alternating blue-green regions from b to g which isolate the second y region from r. This means that the yellow and red regions in that region can swap colors, turning that y region red.
16) Because steps 14 and 15 allow us to recolor both y regions to other colors, we can arrive at a 4-coloring of M-v in which no neighbor of v is yellow. Therefore coloring v = yellow results in a 4-coloring of M. This proves that CASE 2 must also be false. Since both cases are false, M (which was any smallest counter-example) cannot exist proving that there can be no counter-examples, and that all finite planar maps must be 4-colorable.
การแปล กรุณารอสักครู่..
