package acgtk

This module implements a persistent array data structure as described in "A Persistent Union-Find Data Structure" (Sylvain Concohn and Jean-Chrisophe Filliâtre.

It is meant for managing quick access while keeping peristency in backtracking algorithms such as in unification algorithms using union find algorithms.

In particular, when a persistent array a_0 has been modified several times, yielding arrays a_1, a_2, ... , a_N, when a_i is accessed using the get or set functions (with 0 <= i < N) than all a_j with i < j <= N become unaccessible, hence a Unacessible exception is raised.