----------------------------------------
# # 
2 0 
....main....
[ext] H  A type
[ext] H  B type
[ext] H  C type
====
[ext] H; v: A  B  C; v1: A  C

BY dT 2
# 1. [ext] H; v: A  B  C; v1: A  A  B
# 2. [ext] H; v: A  B  C; v1: A; v2: C  C

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