Bond, E. R. and Cundall, P. A. "A Possible PL/I Extension for Mathematical Symbol Manipulation"

Bobrow, D. G. (ed) (1968) Bobrow, D. G. (ed) "Symbol Manipulation Languages and Techniques", Proceedings of the IFIP Working Conference on Symbol Manipulation Languages. North-Holland Publishing Co., Amsterdam, 1968  

Languages mentioned PL/I-FORMAC {1968}