Interval xext = Axis_group_interface::relative_group_extent (elements, common_x, X_AXIS);
Stencil left_br = Horizontal_bracket::make_bracket (me, 10.0, Y_AXIS, LEFT);
Stencil right_br = Horizontal_bracket::make_bracket (me, 10.0, Y_AXIS, LEFT);
Interval xext = Axis_group_interface::relative_group_extent (elements, common_x, X_AXIS);
Stencil left_br = Horizontal_bracket::make_bracket (me, 10.0, Y_AXIS, LEFT);
Stencil right_br = Horizontal_bracket::make_bracket (me, 10.0, Y_AXIS, LEFT);