The Free On-line Dictionary of Computing (30 December 2018):

Early PL/I

    (EPL) A PL/I subset dialect by McIlroy, Morris et
   al, the first running PL/I compiler.  It was used by Bell
   Labs and MIT to write Multics.  EPL had extensions to
   handle the segment/offset nature of Multics pointers.

   See also REPL, TMG.

   ["EPL Reference Manual", Project MAC, April 1966].

   [Sammet 1969, p. 542].

   (1995-11-15)