Erlangen Program at Large-0: Starting with the group SL(2,R)
arXiv:math/0607387
Abstract
This is an easy-reading which describes few geometric invariants which can be obtained from the group SL(2,R) within the Erlangen program of F.Klein.
AMS-LaTeX, 9 pages, 8 figures; v2: small improvements; v3: small corrections, more links to Wikipedia added; v4: minor corrections, two references added