1·Limit — Reasonability of Infinitesimal Calculus.
极限——微积分的合理性。
2·This is normal, and the arbitrary function all can approach with dividing section multinomials because can know from infinitesimal calculus.
这是正常的，因为从微积分可以知道，任一函数都可以用分段多项式来逼近。
3·For if these increases of income or utility are reduced to being infinitesimal, one can use both the symbolism and the powerful manipulations of the differential calculus.
因为，如果这些收入或效用的增加可以化为无穷小，那我们既能使用符号表示，也能利用微分学强大的操作了。