(function(baselib) {






    // Union/find for circular equality testing.

    var UnionFind = function() {
	// this.parenMap holds the arrows from an arbitrary pointer
	// to its parent.
	this.parentMap = baselib.hashes.makeLowLevelEqHash();
    }

    // find: ptr -> UnionFindNode
    // Returns the representative for this ptr.
    UnionFind.prototype.find = function(ptr) {
	var parent = (this.parentMap.containsKey(ptr) ? 
		      this.parentMap.get(ptr) : ptr);
	if (parent === ptr) {
	    return parent;
	} else {
	    var rep = this.find(parent);
	    // Path compression:
	    this.parentMap.put(ptr, rep);
	    return rep;
	}
    };

    // merge: ptr ptr -> void
    // Merge the representative nodes for ptr1 and ptr2.
    UnionFind.prototype.merge = function(ptr1, ptr2) {
	this.parentMap.put(this.find(ptr1), this.find(ptr2));
    };



    baselib.UnionFind = UnionFind;

})(this['plt'].baselib);