### 3.7.115. Hall interval

A constraint for which some filtering algorithms take advantage of Hall intervals. Given a set of domain variables, a Hall set is a set of values $H=\left\{{v}_{1},{v}_{2},\cdots ,{v}_{h}\right\}$ such that there are $h$ variables whose domains are contained in $H$. A Hall interval is a Hall set that consists of an interval of values (and can therefore be specified by its endpoints).