# down 1;;
----------------------------------------
# # 
0 1 
....main....
[ext] H  A type
====
[ext] H  (A  False) type

BY 

++++++++++
- : unit = ()
# refine dT 0;;
----------------------------------------
# # 
1 0 
....main....
[ext] H  A type
====
[ext] H  (A  False) type

BY dT 0
# 1. [ext] H  A type
# 2. [ext] H  False type

++++++++++
- : unit = ()
# 