Point(1) = {0,0,0,1} ;
Point(2) = {1,0,0,1} ;
Point(3) = {1,1,0,1} ;
Point(4) = {0,1,0,1} ;

Line(1) = {1,2} ;
Line(2) = {2,3} ;
Line(3) = {3,4} ;
Line(4) = {4,1} ;

Line Loop(5) = {1,2,3,4} ;

Plane Surface(10) = {5} ;

Physical Surface(1) = {10} ;
