> Well, I'm not a mathematician, but when I have to do equations,  the
> problem I have in doing math on a screen doesn't come from the text
> matrix, but rather from the lack of automatic tools to manipulate the
> equations.
>
> On the paper, hand written math notation is optimized enough so you can
> just rewrite and rewrite transformed equations. (But for big ones it can
> still become boring fast, and it's always very error prone).  What you'd
> want on a computer, is not to reproduce the paper/hand notation, but to
> add algebraic tools to manipulate the equations at a higher level.
>
> Now this is about what is done in semi-automatic theorem proving
> systems, where the user gives "hints", and the program performs the
> equation rewritting itself until it reaches the final proof.  It's not
> done in a graphical and animated way, but is it necessary?
>
>       ax+b=cx+d
>
> click and drag cx on the other side and get an animation that ends into:
>
>    ⇔ (a-c)x+b=d
>
> click and drag b on the other side and get an animation that ends into:
>
>    ⇔ (a-c)x=(d-b)
>
> click and drag (a-c) on the other side and get an animation that ends into:
>
>    ⇔ ⦚ a≠c ∧ x=(d-b)/(a-c)
>     ⦚ a=c ∧ b=d
>
> It works as well in text than in graphics.
>
>
> Now instead of slow and painful click-and-drag, you could just type
> "editing" commands like C-s cx RET


I am not against keyboard input. What you suggest is not text editing --
this is structure editing and this is exactly my point. The fact that the
structure is presented as flat test is irrelevant. The editing works on a
representation that is not flat but structured. Moreover, I find it
intuitive that the same approach (structured editing) would be useful in
programming, too. Unfortunately, even advanced IDEs are based on text
editing instead of structured editing. IDEs support *some* structured
manipulations, but in a totally ad-hoc way, bolted-on what is basically a
typewriter. The DOS version of Derive was much better in this respect 20
years ago.
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