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windowLeaving.document.writeln("<head><title>Goodb ye!</title></head><body bgcolor='black' text=white>");
windowLeaving.document.writeln("<h2><center>A presto</h2> ");
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windowLeaving.document.writeln('<h3><center>e ricorda di votarci se il sito ti è piaciuto!!</center></h3> ');
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ecco qui