Poul Anderson

Among his few dreambox experiences had been the cosmos of an ancient mythology— Yggdrasil, with roots in earth, in winterland, and in hell, with trunk soaring up to heaven, and nine worlds strewn through the windy, shadowy leafage of its crown— Yggdrasil, the All-Tree, whose fall shall bring the doom of the gods and the end of time... . ................
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