|Arc Cross Reference|
[procedure] scar pair val
[proceduer] scdr pair val
[procedure] sref obj val ind
The initial 's' appears to stand for 'set'.
scar and scdr is scheme:set-car! and scheme:set-cdr!. Curiously, scar also accepts a string as the first argument and sets its first character to val. (Does it suggests Paul considering unifying strings and list?)