[TUHS] yacc for Unix v5

I've been looking into the history of yacc (yet another compiler compiler). The earliest reference I can find is the man page for yacc from v3 which indicates that yacc was written in B language. The files actn.b and /crp/scj/bigyacc are mentioned. No luck so far in locating those files. There is a man page for v4 which is very brief. There is a yacc executable for v5 but so far I haven't found any v5 era code that works with it. My attempts to compile bc.y from v6 using yacc from v5 were not successful. Also the source code for yacc in v5 is missing. On a happier note I was able to use yacc and cc to regenerate the bc calculator in v6. It needed a fair amount of swap space to compile otherwise an "Intermediate file error" will occur. It seemed to require at least 300 blocks of hard drive space. It's a bit mysterious what the Unix v5 yacc was used on. It predated bc and expr. There's no v5 era *.y files available to look at. Mark