the proof is easy, but the counterexamples are hard . 证明是容易的,但反例则甚难。
a brief discussion on the function of counterexample in discrete mathematics teaching 谈反例在离散数学教学中的作用
a counterexample on the existence of positive periodic solutions for two-species predator-prey diffusive systems 食饵系统正周期解存在性的一个反例
in a sense this program is a counterexample, in that it is never useful as a filter 从某种意义上,这个程序是一个可执行文件,因为对于作为过滤器来说,它决不会有任何用处。
there is an old saying : large wealth of a family can not last longer than three generations . is there any counterexample in the history 有句话是“富不过三代”。历史上有没有富豪延续超过三代的例子?