# Elementary Calculus: An Infinitesimal Approach by Keisler Hacker Approved page: https://hackerapproved.com/p/elementary-calculus-an-infinitesimal-approach/ 3 people recommended Elementary Calculus: An Infinitesimal Approach by Keisler in Hacker News comments and none criticized it, November 2025 to October 2026. It was recommended in 2 of 12 months, in 2 threads. It does not meet the Hacker Approved badge rule. 2 of the 3 people who recommend it commented in one thread, “Simplifying and Refactoring Introductory Calculus”. **Verdict:** People recommend it as a fairly well-regarded calculus textbook that is available online. Summary written by Claude from 1 comment. ## Why people recommend it - Well-regarded calculus textbook (1 comment in the sample): "there's a fairly well-regarded textbook available online" ([source](https://news.ycombinator.com/item?id=49719434)) ## Other calculus textbooks people recommend - [Calculus by James Stewart](https://hackerapproved.com/p/calculus/): 9 recommend, 1 mixed, 3 criticize - [Calculus Made Easy by Silvanus P. Thompson](https://hackerapproved.com/p/calculus-made-easy/): 5 recommend, 0 mixed, 1 criticize - [Calculus for Mathematicians, Computer Scientists, and Physicists by Daniel Flegg](https://hackerapproved.com/p/calculus-for-mathematicians-computer-scientists-and-physicists/): 4 recommend, 0 mixed, 4 criticize ## The badge A product earns the Hacker Approved badge when at least 10 people recommend it, recommenders outnumber critics at least 2 to 1 (mixed feelings count toward neither side), it was recommended in at least 4 of the 12 months and in at least 5 different threads, and no single thread supplies more than half of the people who recommend it. Health and money products are never badged. ## Cite as Hacker Approved, "Elementary Calculus: An Infinitesimal Approach by Keisler", https://hackerapproved.com/p/elementary-calculus-an-infinitesimal-approach/ (3 recommend, 0 mixed, 0 criticize; Hacker News comments, November 2025 to October 2026). Counts updated 3 Nov 2026, with data through October 31, 2026.