Robin POPplestone, Edinburgh, 1967.
An innovative language incorporating many of Landin's ideas, including streams, closures, and functions as first-class citizens.
The first implementation was named Multi-POP, based on a REVPOL function written in POP-1, producing the reverse-polish form as output.
"POP-2 Papers", R.M.
Burstall et al, Oliver & Boyd 1968.
"Programming in POP-2", R.M. Burstall et al, Edinburgh U Press 1971.
"POP-2 User's Manual", R. Popplestone, Mach Intell 2, E. Dale et al eds, Oliver and Boyd, Edinburgh 1968.