Implementation of an incident list based graph representation.
Implementation of an incident list based graph representation. This trait is common to
both the immutable and mutable variants. An incidence list based representation speeds up
traversing the graph along its paths by storing the list of connecting edges at each node.
Implements an incident list based immutable graph representation.
Wrapper class mimicking a scala.collection.immutable.Set
without copying the contents of the underlying EqHashMap.