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1670s as a technical term in perspective drawing; 1706 as "drawing, sketch, or diagram of any object," from French plan "ground plan, map," literally "plane surface" (mid-16c.), from Latin planum "level or flat surface," noun use of adjective planus "level, flat" (see plane (n.1)). The notion is of "a drawing on a flat surface." Meaning "scheme of action, design" is first recorded 1706, possibly influenced by French planter "to plant," from Italian planta "ground plan."
Programming Language for Allocation and Network Scheduling. A PL/I preprocessor, used for developing scheduling algorithms. "A User's Guide to the Programming Language for Allocation and Network Scheduling", H.R. Ramsey et al, TR SAI-77-068-DEN, Science Applications Inc (Jun 1977).