1. On the structure of the polynomial time degrees;Ambos-Spies,1984
2. Sublattices of the polynomial time degrees;Ambos-Spies;Inform. and Control,1985
3. On the relative complexity of subproblems of intractable problems;Ambos-Spies,1985
4. Three theorems on polynomial time degrees;Ambos-Spies,1985
5. Polynomial degrees of NP-sets;Ambos-Spies,1987