intro:
|----------------------------------------------------------|
|----------------------------------------------------------|
|--------------------------------0-------------------------|
|-------2---0-(0-2)--------2-0-2---------2---(0-2)---------|
|---------2-----------------2--------------2---------------|
|---0-0----------------0-0-----------0-0-------------------|
|--------------------------------------------------------------|
|--------------------------------------------------------------|
|0-0-2-(2-3)--2-0-2--------------------------------------------|
|-2------------------------------------------------------------|
|--------------------------------------------------------------|
|--------------------------------------------------------------|