Please, accept our apologies for the late reply.
In order to apply a theme for our controls in WPF, you don't need a separate theme assembly since the themes are part of the controls' assemblies.
If you have further questions please do not hesitate to ask us.
I hope this will help you.
And by the way, if you want to reduce the size of your Silverlight app, you should check our latest Silverlight tool - Assembly Minifier (http://blogs.telerik.com/blogs/posts/10-06-10/telerik_assembly_minifier.aspx
the Telerik team
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