cl__1 = 2.5;
Point(1) = {0, 0, 0, cl__1};
Point(2) = {0, 10, 0, cl__1};
Point(3) = {0, 50, 0, cl__1};
Point(4) = {50, 50, 0, cl__1};
Point(5) = {50, 0, 0, cl__1};
Point(6) = {10, 0, 0, cl__1};
Point(9) = {10, 10, 0, cl__1};
Line(1) = {1, 2};
Line(2) = {2, 3};
Line(3) = {3, 4};
Line(4) = {4, 5};
Line(5) = {5, 6};
Line(6) = {6, 1};
Line(7) = {2, 9};
Line(8) = {9, 6};
Line Loop(1) = {1, 2, 3, 4, 5, 6};
Plane Surface(1) = {1};

Line {7} In Surface {1};
Line {8} In Surface {1};

Recombine Surface {1};
Physical Line(100) = {1,2,3,4,5,6};
Physical Surface(100) = {1};

Mesh.Algorithm = 8;
Mesh.RecombineAll = 1;
Mesh.CharacteristicLengthFactor = 5.0;
Mesh.SubdivisionAlgorithm = 1;
Mesh.Smoothing = 20;