what is christopher paolini's 4th book of the inheritance cyle called??..

i would have to guess "Aren". In the third installment, the ring his father gave him which was a gift from the elves has enormous amounts of power and energy inside it. Eragon was not able to use the ring's full potential during the third book. Its only fitting that the last book be named after the memory of his father. aren is an indispensable tool Eragon can use against the fight with King Galbatorix. I'm guessing it would be his ultimate weapon against the dark king.