Selling performing assets to American / any other banks helps to ring fence toxic assets within $DB. At that point the "good banks" are no longer held by $DB.
The extension of this is the $DB - $CRZBY merger. Since the German government already owns a large percentage of $CRZBY the government would use the same mechanism to channel huge amounts of additional bailout Euros into the newly formed Deutsche-Commerzbank.
The whole $DB - $CRZBY merger is simply a proposition to buy time by kicking the can down the road. Its not designed to resolve the outstanding issues.
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