create 4 4 .
push_back_column 4 y e d r
pop_back_column
pop_back_row
set 2 0 w
set 0 2 j
push_back_row 4 a l v h
set 0 1 g
get 2 2 .
push_back_row 4 t s j h
get 0 1 g
pop_back_row
get 2 0 w
set 1 3 k
push_back_row 4 c w q a
push_back_column 5 f z d n z
get 4 0 c
set 4 2 f
pop_back_column
push_back_column 5 f x l t r
get 1 4 x