COMMENT ⊗   VALID 00002 PAGES
C REC  PAGE   DESCRIPTION
C00001 00001
C00002 00002	Let %2mapstack[u,f] ← qif qn u qthen qnil qelse f[u,mapstack[qd u,f]]%1.
C00003 ENDMK
C⊗;
Let %2mapstack[u,f] ← qif qn u qthen qnil qelse f[u,mapstack[qd u,f]]%1.
Show that ⊗mapcar, ⊗maplist, ⊗mapapp, and ⊗mapchoose can all be defined
in terms of ⊗mapstack.