PL/I - Wikipedia
https://en.wikipedia.org/wiki/PL/I
PL/I is a procedural, imperative computer programming language developed and published by IBM. It is designed for scientific, engineering, business and system programming. It has been used by academic, commercial and industrial organizations since it was introduced in the 1960s, and is still used.
PL/1 programming language
http://www.softpanorama.org/Lang/pl1.shtml
PL/1 Programming Language. The Cobol replacement that never took of the ground except in... Exceptions in PL/1 Multiple entries in procedures
PL1 File Extension - What is a .pl1 file and how do I open it?
https://fileinfo.com/extension/pl1
A PL1 file contains a building floor plan created with 3D Home Architect Deluxe. It includes the first-floor layout, as well as objects, such as furniture, lighting, appliances, and window treatments.
PL1! Charts and Quotes — TradingView
https://www.tradingview.com/symbols/NYMEX-PL1!/
PL1! Platinum Futures NYMEX. Using Fibonacci Speed/Resistance Fan to Manage Trending Trades. PL1!