cumulative translation

<svg width="500" height="500" xmlns="http://www.w3.org/2000/svg" xmlns:svg="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<rect x="0" y="0" width="500" height="500" id="fond" fill="#dd000d"/>
<g>
<g>
<rect x="100" y="100" width="50" height="50" id="cobaye"/>
<animateTransform attributeName="transform" type="translate" values="100" begin="bou1.mousedown" dur="0s" />
</g>
<animateTransform attributeName="transform" type="translate" values="100" begin="bou2.mousedown" dur="0s" />
</g>
<rect x="100" y="400" width="50" height="50" id="bou1" fill="#ffffff"/>
<rect x="200" y="400" width="50" height="50" id="bou2" fill="#ffffff"/>
</svg>