Simplices with equiareal faces.

link: http://arxiv.org/abs/0909.1859
Abstract

We study simplices with equiareal faces in the Euclidean 3-space by means of
elementary geometry. We present an unexpectedly simple proof of the fact that,
if such a simplex is non-degenerate, than every two of its faces are congruent.
We show also that this statement is wrong for degenerate simplices and find all
degenerate simplices with equiareal faces.