希尔伯特第十四问题 hilbert's fourteenth problem

四色问题 four color problem ; Four-color problem

十四的质问 Chapter Sixty Six

四处询问 ask around

四阶边值问题 fourth-order boundary value problem ; fourth-order bvp

存在四个问题 There are four problems

四色方柱问题 Instant Insanity

第四个问题 The fourth issue

奇异四阶边值问题 fourth order singular boundary value problem ; singular fourth-order boundary value problem

人生的四个经典问题 Four Classical Questions in Life