1. NB. Due to the lack of space we cite only papers from which all other references mentioned in this survey can be found.
2. Aanderaa, S.O., Börger, E. [1981]: The equivalence of Horn and network complexity for Boolean functions. Acta Informatica (to appear)
3. Aanderaa, S.O., Börger, E., Lewis, H.R. [1981]: Conservative reduction classes of Krom formulas. The Journ. of Symb. Logic (to appear)
4. Börger, E. [1975]: On the construction of simple first-order formulae without recursive models. Proc. Coloquio sobra logica simbolica, Madrid, 9–24
5. — [1979]: A new general approach to the theory of the many-one equivalence of decision problems for algorithmic systems. ZMLG 25, 135–162