1. Universal Algebra;Cohn,1965
2. Combinatorial Functors;Crossley,1974
3. Effective dimension;Crossley;J. Algebra,1977
4. On the factorization of polynomials in a finite number of steps;Fro¨hlich;Math. Z.,1955
5. Effective procedures in field theory;Fro¨hlich,1956