[TYPES] A geometry problem for proof systems
Peter Freyd
pjf at saul.cis.upenn.edu
Thu Sep 22 06:53:26 EDT 2005
Yong Lua asks if the following is a theorem:
A triangle with two internal angle bisectors of equal length is
an isosceles triangle.
When I was asked this by a fellow high school student (thousands of
years ago) I gave him a long, quite ugly, computational proof (which
did not, alas, satisfy her notion of proof).
I've never seen a proof other than the ugly one.
These days, of course, one just asks Google. The query:
angle bisector isosceles
leads one to
www.mathpages.com/home/kmath433.htm
It has the ugly proof.
Peter
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