The mathematicians turned to culling periodic solutions. 數學家們轉而去挑選周期解。
Culling stem cells destroys the days-old embryo harboring them, regardless of whether it was cloned or left over in a fertility clinic. 一般來講，無論是被克隆還是被轉移到其他環境中，挑選干細胞線將會自動破壞曾經養育它的胚胎。