However, David Zuckerman showed in 1996 that every one of these 21 problems has a constrained optimization version that is impossible to approximate within any constant factor unless P = NP, by showing that Karp's approach to reduction generalizes to a specific type of approximability reduction.
Međutim, David Zuckerman je pokazao 1996. da je svaki od ovih 21 problema ima ograničenu optimizovanu verziju koja je nemoguće približiti stalnom faktoru osim P = NP,pokazujući da je Karpov pristup smanjenju generalizuje na određenu vrstu aproksimacije smanjenja.