The Free On-line Dictionary of Computing (30 December 2018):

Linear Graph Notation
LGN

   (LGN) A linearised representation of TCOL trees.

   [B.W. Leverett et al, "An Overview of the Production Quality
   Compiler-Compiler Projects", TR CMU-CS-79-105, Carnegie Mellon
   1979].

   (1995-01-23)