thank you for help. my summary for 5.5.0.Final:<div><br></div><div>1. <b>Esteban&#39;s suggestion works</b>, but of course requires more activations</div><div>2. Wolfgang&#39;s suggestion to <b>use java dialect</b> works</div>
<div>3. it looks like there is <b>no way to achieve the same with mvel</b> dialect</div><div><br></div><div>sincerely,</div><div>Martin<br><br><div class="gmail_quote">2012/11/30 Esteban Aliverti <span dir="ltr">&lt;<a href="mailto:esteban.aliverti@gmail.com" target="_blank">esteban.aliverti@gmail.com</a>&gt;</span><br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>rule &quot;Remove all but one&quot;</div><div>when</div><div>    $f1: Fact(id == &quot;aaa&quot;)</div><div>    $f2: Fact(id == &quot;aaa&quot;, this != $f1)</div>



<div>then</div><div>    retract($f2);</div><div>end</div></blockquote></div><br></div>