Earlier quoted context omitted.
Mostly likely your PDP-1 assembly is a little rusty, so that may be hard to read in isolation. Refresh your memory with the original manual: http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp1/F1... (Actually that just documents the hardware. Honestly I don't know if the assembler that built Spacewar still survives.)
"Refresh your memory". I liked that one. Seriously though, check the following out for the PDP-1 Macro Assembler manual: http://bitsavers.trailing-edge.com/pdf/dec/pdp1/PDP-1_Macro....
Right, but is the DEC assembler the one in use at MIT? My memory (mostly from reading Hackers) is that their toolchain was a homebrew thing.