<?xml version="1.0"?>
<geometry>

  <surface id="1" type="x-plane" coeffs="-10" boundary="vacuum" />
  <surface id="2" type="x-plane" coeffs="-7" />
  <surface id="3" type="x-plane" coeffs="-4" />
  <surface id="4" type="x-plane" coeffs="4" />
  <surface id="5" type="x-plane" coeffs="7" />
  <surface id="6" type="x-plane" coeffs="10" boundary="vacuum" />
  <surface id="7" type="x-plane" coeffs="0" />

  <surface id="11" type="y-plane" coeffs="-10" boundary="vacuum" />
  <surface id="12" type="y-plane" coeffs="-7" />
  <surface id="13" type="y-plane" coeffs="-4" />
  <surface id="14" type="y-plane" coeffs="4" />
  <surface id="15" type="y-plane" coeffs="7" />
  <surface id="16" type="y-plane" coeffs="10" boundary="vacuum" />
  <surface id="17" type="y-plane" coeffs="0" />

  <cell id="1" material="1" region="3 -4 13 -14" />
  <cell id="2" material="2" region="2 -5 12 -15 ~(3 -4 13 -14)" />
  <cell id="3" material="3" region="(1 -7 17 -16 | 7 -6 11 -17) (-2 | 5 | -12 | 15)" />
  <cell id="4" material="4" region="((1 -7 11 -17) | (7 -6 17 -16)) ~(2 -5 12 -15)" />

</geometry>
