 
Summary: LEVI EQUATION FOR ALMOST
COMPLEX STRUCTURES
Giovanna Citti Giuseppe Tomassini
Contents
1. Introduction and generalities.
Let (R4
, J) be the space R4
equipped with an almost complex structure J. We
recall that J is a differentiable map R4
GL(4, R) such that J(p)2
= Id,
for every p R4
. Let M be a differentiable hypersurface in R4
. For every
p M the tangent hyperplane TpM contains a (unique) Jinvariant plane
TJ
p M. The distribution of planes p TJ
p M is called the Levi distribution
on M, and M is said to be JLevi flat whenever p TJ
p M is integrable. In
