The Citadel is an archive of information for George R.R. Martin's A Song of Ice and Fire.
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GRRM also revealed that aFoC will hopefully span the next 5/6 years so that aDwD can begin where he expected it to do so all along.
He also heavily suggested that characters that will spend their time learning in the next 5/6 years will not feature very much in the next book. But all current POVs will appear. So one can assume that we wouldn't get more than one or two Arya/Bran chapters.
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