Published online by Cambridge University Press: 17 September 2020
We consider the problem of finding two free export/import sets $E^+$ and
$E^-$ that minimize the total cost of some export/import transportation problem (with export/import taxes
$g^\pm $), between two densities
$f^+$ and
$f^-$, plus penalization terms on
$E^+$ and
$E^-$. First, we prove the existence of such optimal sets under some assumptions on
$f^\pm $ and
$g^\pm $. Then we study some properties of these sets such as convexity and regularity. In particular, we show that the optimal free export (resp. import) region
$E^+$ (resp.
$E^-$) has a boundary of class
$C^2$ as soon as
$f^+$ (resp.
$f^-$) is continuous and
$\partial E^+$ (resp.
$\partial E^-$) is
$C^{2,1}$ provided that
$f^+$ (resp.
$f^-$) is Lipschitz.