From: LordBeotian on
Given two vector fields on R^2 V and W consider the vector field given
by the difference V-W.
If V and W are always nonzero can V-W have nontrivial periodic orbits?
From: Robert Israel on
LordBeotian <pokipsy76(a)yahoo.it> writes:

> Given two vector fields on R^2 V and W consider the vector field given
> by the difference V-W.
> If V and W are always nonzero can V-W have nontrivial periodic orbits?

Hint: if F(x,y) = [F_1, F_2] is a vector field on R^2, then
F + [F_1^2 + 1, 0] and [F_1^2 + 1, 0] are nonvanishing.
--
Robert Israel israel(a)math.MyUniversitysInitials.ca
Department of Mathematics http://www.math.ubc.ca/~israel
University of British Columbia Vancouver, BC, Canada