As I understand it the load of supporting two libraries was too much work, also the alef (and perhaps limbo) experience lead to libthread which provides much of the same functionality - abet not quite as neatly.
the sources of the 2nd edition alef have been released and there was a one line change to make the code work on the 3rd (and I assume 4th) editions - the memory layout of processes has changed a little and the alef library needs to know (the stack address I think), for the fix see 9fans passim. -Steve
