cl__1 = 0.1;
Point(0) = {0, 0, 0, cl__1};
Point(1) = {1, 0, 0, cl__1};
Point(2) = {1, 1, 0, cl__1};
Point(3) = {0, 1, 0, cl__1};
Spline(0) = {0, 1};
Spline(1) = {1, 2};
Spline(2) = {2, 3};
Spline(3) = {3, 0};

//
// fails
//
Line Loop(0) = {0, 1, 2, 3};
Ruled Surface(0) = {0};

//
// works
// seems that gmsh has a problem with a line loop that has index 0
//
//Line Loop(1) = {0, 1, 2, 3}; 
//Ruled Surface(0) = {1};
