This paper presents a new formalism for irregular pyramids based on combinatorial maps. Such pyramid consists of a stack of successively reduced graph. Each smaller graph is deduced from the preceding one by a set of edges which have to be contracted or removed. In order to perform parallel contractions or removals, the set of edges to be contracted or removed has to verify some properties. Such a set of edges is called a Decimation Parameter. A combinatorial map encodes a planar graph thanks to two permutations encoding the edges and their orientation around the vertices. Combining the useful properties of both combinatorial maps and irregular pyramids offers a potential alternative for representing structures at multiple levels of abstraction.
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