EP1. 乘法与加法的思维方式 EP2.微积分 EP3.庞加莱猜想——For a topologist,all these shapes-sorry-these manifolds can be created from each other by deformation; therefore they are identical,or rather"homeomorphic",as they say in these parts.So a ball and a cube are homeomorphic manifolds,as are a vase and a plate,which are basically just balls which have been deformed!This is why topologists sometimes put flowers in completely flat vases,which is difficult for the flowers which know nothing about topology.