another-take…

cube_two_materials.geo
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			L = 1;
			s = 0.4;

			Point(1) = {-L/2., -L/2., 0, s};

			line[] = Extrude{L,0,0}{ Point{1}; };
			surface[] = Extrude{0,L,0}{ Line{line[1]}; };
			volume[] = Extrude{0,0,L}{ Surface{surface[1]}; };

			Physical Volume(1) = {volume[1]};

			Transfinite Surface "*";
			Recombine Surface "*";
			Transfinite Volume "*";