SOCRATES: A highly efficient automatic test pattern generation system. An automatic test pattern generation system, SOCRATES, is presented. SOCRATES includes several novel concepts and techniques that significantly improve and accelerate the automatic test pattern generation process for combinational and scan-based circuits. Based on the FAN algorithm, improved implication, sensitization, and multiple backtrace procedures are described. The application of these techniques leads to a considerable reduction of the number of backtrackings and an earlier recognition of conflicts and redundancies. Several experiments using a set of combinational benchmark circuits demonstrate the efficiency of SOCRATES and its cost-effectiveness, even in a workstation environment.