1:      1  1 CALL pred mapinit.main/2-0 (det) mapinit.m:28
mdb> echo on
Command echo enabled.
mdb> step
       2:      2  2 CALL pred mapinit.xmap_init/1-0 (det) mapinit.m:37 (mapinit.m:29)
mdb> finish
       5:      2  2 EXIT pred mapinit.xmap_init/1-0 (det) mapinit.m:37 (mapinit.m:29)
mdb> dd -d 3 -n 7
xmap_init(empty)
Valid? y
No bug found.
       5:      2  2 EXIT pred mapinit.xmap_init/1-0 (det) mapinit.m:37 (mapinit.m:29)
mdb> c
two(0, "zero", empty, empty)