> pss("square", 5L, nrow = 7, ncol = 9)
/ - - - - - - - - - \ 
| 2 3 4 5 1 2 3 4 5 | 
| 1 2 3 4 5 1 2 3 4 | 
| 5 1 2 3 4 5 1 2 3 | 
| 4 5 1 2 3 4 5 1 2 | 
| 3 4 5 1 2 3 4 5 1 | 
| 2 3 4 5 1 2 3 4 5 | 
| 1 2 3 4 5 1 2 3 4 | 
\ - - - - - - - - - / 

