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[paragraph about how great the set is otherwise]"A third innovation concerned memory loss. Earlier computer programming had followed the principle that when one routine hands over control to another it instantly forgets everything it had needed to know about the local context while it was working. After all, why waste memory space? However, instant memory loss on the relinquishing of control would make recursive routines impossible."This is generally but not *strictly* true. Tail recursion is free from this limitation, which is why some programming languages optimize tail calls. These then support indefinite depths of recursion in such cases. A decent formal description of the same can be found in the most recent standard for Scheme, herehttp://www.r6rs.org/final/html/r6rs/r6rs-Z-H-14.html#node_sec_11.20