Examples include contradictory contracts where one clause directly negates another clause, or conflicts between fundamental (e.g. constitutional) legal norms. Leibniz's 1666 doctoral dissertation "De casibus perplexis" (Perplexing Cases) is an early study of contradictory legal conditions. In domestic law, it has been argued that the German Constitutional Court confronted a legal dilemma when determining, in connection with proceedings relating to the German Aviation Security Act, whether a government official could intentionally kill innocent civilians by shooting down a hijacked airplane that would otherwise have crashed into a football stadium, killing tens of thousands.