Hi Marc-Olivier. I think this should work:
<$reveal type="nomatch" state=<<folded-state>> text="hide" tag="div" retain="yes" animate="yes">
<div class="tc-subtitle">
<$link to={{!!modifier}}>
<$view field="modifier"/>
</$link>
<$view field="created" format="date" template={{$:/language/Tiddler/DateFormat}}/>
<$list filter="[{!!modified}!prefix{!!created}]">
(<$view field="title" format="date" template={{$:/language/Tiddler/DateFormat}}/>)
</$list>
</div>
</$reveal>
BUT, if I recall, a tiddler is always treated as modified as it is created so you always get both dates showing with this. I think there has been discussion about this but I'm not sure what the reason is behind it.
<:-)