1. The logical schemes of algorithms;Ianov;Problems of Cybernetics (USSR),1960
2. The undecidability of the equivalence problem for program schemata;Luckham;Bolt, Beranek and Newman Inc., Report No. 1141, Santa Ana, Calif.,1964
3. A basis for a mathematical theory of computation;McCarthy,1963
4. Equivalence Problems in a Model of Computation;Paterson,1967