How to generalize the
Fano" = Klein equation ?
there is a transitivity hierarchy (stick-n-stuck-all structures)
1....... groups, affine spaces with translations
1+ ... affine spaces with translations and dilatations
2...... lines, fields
3...... projective lines
3+.... also projective lines
4,5.... the sporadic Mathiew groups.
After groups and fields, the next symmetric objects are the projective lines.
Reading from the Conway-Hulpke-Mckay table :
9T27 - sharply triple transitive, the natural projective line with 9 points
and
9T32 - triple transitive, but also a projective group PgamaL(2,
.
The extra-transitivity (more than three) of a projective line is explained by some twists of the line. Let' s say that the line is coordinated with some elements of a field; then, the automorphisms of that field will permute also the points on the line.
http://en.wikipedia.org/wiki/CollineationThe nice case is p prime, when
ProjectiveLine(p prime)'''= Lin (stick three stuck all)
for p^k +1 points on the projective line,
ProjectiveLine(p^k)''' = Cyc[k](Lin). (stick three and reach the twisting)
that Gal(K/k) is cyclic of order k
An affine line should be also twisted by field automorphisms,
for example
9T15 - the affine line on 9 points, sharply 2-transitive (order 72)and
6T19 - the affine line with twists (order 144)