[plt-scheme] stable sort

There's no stable sort available?  I searched for "sort" in Help Desk
and got

(sort less-than?-proc list) PROCEDURE 
This is the same as mergesort (see section 21) with the arguments
reversed.

(mergesort list less-than?) PROCEDURE 
Sorts list using the comparison procedure less-than?. This
implementation is not stable (i.e., if two elements in the input are
``equal,'' their relative positions in the output may be reversed).

(quicksort list less-than?) PROCEDURE 
Sorts list using the comparison procedure less-than?. This
implementation is not stable (i.e., if two elements in the input are
``equal,'' their relative positions in the output may be reversed).

S.