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Introduction. A configuration (m ci ni)is a set of m points and n lines in a plane, with d of the points on each line and c of the lines through each point; thus cm = dn. Those permutations which preserve incidences form a group, "the group of the configuration." If m -n, and consequently c = d, the group may include not only symmetries which permute the points among themselves but also reciprocities which interchange points and lines in accordance with the principle of duality. The configuration is then "self-dual," and its symbol («<*, n

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