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By chance, I noted that my daughter Pénélope’s math-book had exercises for geometry “with software”. So I gave it a try with her: she manipulates the mouse and tries… I just guide. It worked real well!

It worked well because she understood extremely fast the little hints “you are selecting this line” or “this point”. That is a the proof of a very mature software… it could be more elegant (e.g. lines were much too thin for such starting pictorials) but that didn’t prevent her usage at all.

She then was motivated by the dynamic geometry system’s effect of moving things around, hiding and still having the constraints…

We wanted then to proof if two things were perpendicular or of same length… and Cabri asserted it. Great for her!

Then back to the homework: a formal justification needs to be written.