1. Automata on a two dimensional tape;Blum,1967
2. Array automata and array grammars;Milgram,1971
3. On the definition and recognition of patterns in discrete spaces;Mylopoulos,1970
4. On the recognition of topological invariants by 4-way finite automata;Mylopoulos;Comp. Graph. Image Proc.,1972
5. Connectivity in digital pictures;Rosenfeld;JACM,1970