[TUHS] History of cal(1)?

[Dan Cross via TUHS <tuhs@tuhs.org>]

Over on the Multicians list, Jeffrey Johnson asked a question about
the Multics `calendar` program, which was written by Tom van Vleck in
Dec, 1973. Despite what some man pages say, the analogous Unix `cal`
program appears to have arrived in the 5th Edition (mid 1974).
Jeffrey's question was whether `cal` was inspired by `calendar`?

My suspicion is that it was not, and this is a case of parallel
invention: after all, a program that prints out a calendar is
obviously useful.  I also suspect that program, or something
substantially similar, had existed for quite a while before someone
tossed it into /usr/source/s1 in time for 5th Edition.  Does anyone
recall who wrote it, and when?

But this also rekindles my curiosity about something I've always
wondered: what _was_ the level of communication between the folks at
Bell Labs and the Multics people after 1969?  By all accounts,
individuals remained friendly and collegial with one another, but it
seems like communication (let alone collaboration) between the two
"camps" was minimal.  Is that accurate?

        - Dan C.