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您的行的问题proof在于它proof旨在应用一些默认规则。在上面的证明中,Isabelle 无法弄清楚你想要进行存在性介绍。因此,您可能想明确告诉系统这样做,例如,通过继续使用类似proof (intro exI).
proof
proof (intro exI)
我希望这会有所帮助,勒内