Hmmm, infinitesimal calculus.
I would have loved if you had added vertical in brackets following the dotted lines in your second diagram to avoid confusion. In my eyes originally, your dotted lines also appeared as small dashed lines. So i was seeing dotted lines (relatively) everywhere and wondering the one you were referring to, until i made sense of it with the math.
Nice piece of writing though.
Nice seeing you here
That is a good point. I will keep it in mind for a next analysis post ^^