Things are coexistent when in empirical intuition the perceptions of them can follow upon one another reciprocally. 如果在经验性的直观中一事物的知觉能够与另一事物的知觉交互继起，这些事物就是同时的。
The approach is more practical and less abstract than other Calculus books, while conserving a perfect balance between mathematical rigor and intuition. 这本书比其他微积分书要更实用而且更易懂，同时在数学的直观和严格方面保持了绝妙的平衡。
