(1) The ICL 1900 PLAN Reference Manual, (ICL Technical Publications 4004 and 4322) and 1900 PLAN Supplement, by D C Toll (Atlas Computer Laboratory, July 1973).
(2) PL/360, A Programming Language for the 360 Computers by N Wirth, (JACM Vol 15 No 1, Jan 1968).
(3) The 1906A TASK System, by G W Robinson (Atlas Computer Laboratory, October 1973).