The files in c/ come from the last1120c.tar.gz tape at
http://www.tuhs.org/Archive/Applications/Early_C_Compilers/, and form
a working C compiler for 2nd Edition UNIX.

The files in lib/ come from the libc.sa file which is on the last1120c.tar.gz 
tap(I) tape image, also at the same URL, and form the C library for the
above compiler.

The files in cmd/ are recreated from the text fragments found on the file
s1-bits.gz at
http://www.tuhs.org/Archive/PDP-11/Distributions/research/1972_stuff/
These were reconstructed by Doug Merritt and Warren Toomey, and form
the source code to some of the commands on 2nd Edition UNIX.