= Constraint hypergraph
The <hypergraph> whose <vertices> are the <variables> of a <constraint satisfaction problem> and whose <hypergraph edges> are its constraint scopes. Several constraints can have the same scope. An incidence drawing uses extra scope nodes for display; these do not become extra <variables> of the original problem. Ordinary <treewidth> of a <constraint hypergraph> refers to <treewidth> of its <primal graph>, equivalently to a <tree decomposition> covering each whole scope, not to generalized hypergraph width measures.
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