Hello, Which revisions of the "C Reference Manuals" are known to be out there? I found this: https://www.bell-labs.com/usr/dmr/www/cman.pdf Which seems to match the one from V6: https://github.com/dspinellis/unix-history-repo/tree/Research-V6-Snapshot-D… "C is also available on the HIS 6070 computer at Murray Hill and and on the IBM System/370 at Holmdel [3]." But then there's this: https://www.princeton.edu/ssp/joseph-henry-project/unix-and-c/bell_labs_136… "C is also available on the HIS 6070 computer ar Hurray Hill, using a compiler written bu A. Snyder and currently maintained by S. C. Johnson. A compiler for the IBM System/360/370 series is under construction." Due to the description of the IBM compiler, it seems to predate the V6 revision. Both above revisions use the =+ etc operators. Finally, this version edited by Snyder: https://github.com/PDP-10/its/blob/master/doc/c/c.refman "In addition to the UNIX C compiler, there exist C compilers for the HIS 6000 and the IBM System/370 [2]." This version documents both += and =+ operators.