Grob *common = common_refpoint_of_array (figures, me, Y_AXIS);
Interval ext = Axis_group_interface::relative_group_extent (figures, common, Y_AXIS);
Grob *common = common_refpoint_of_array (figures, me, Y_AXIS);
Interval ext = Axis_group_interface::relative_group_extent (figures, common, Y_AXIS);