Completely agree with you here, just want to add that if anyone is looking for a rigorous approach to infinitesimal calculus, check out this book: https://en.wi

Completely agree with you here, just want to add that if anyone is looking for a rigorous approach to infinitesimal calculus, check out this book: https://en.wikipedia.org/wiki/Elementary_Calculus:_An_Infinitesimal_Approach https://en.wikipedia.org/wiki/Elementary_Calculus:_An_Infini... And more generally, look in to "non-standard analysis": https://en.wikipedia.org/wiki/Non-standard_analysis https://en.wikipedia.org/wiki/Non-standard_analysis