I assume you've already seen this, but the CHM blog has this to say:
pp. 145−169
PDP-7 assembly listings for “t1,” “t2,” “t3,” “t4,” “t5,” “t6,” “t7,” and “t8”
Unidentified program.
Perhaps an interpreter for a programming language? B?
https://computerhistory.org/blog/the-earliest-unix-code-an-anniversary-sour…
Thalia