The occupation of bpmf is as follows: b occupies the upper-middle grid of pinyin grid (also called four lines and three grids), and the middle grid does not touch the first line. P occupies the middle and lower case of the pinyin case, and does not touch the fourth line, and the middle case is full. M occupies the middle grid and touches the second and third lines, that is, fills the middle grid, and f occupies the upper grid and does not touch the first line. Bend vertically in the middle of the upper case and start writing until the third line, and cross the second line in the middle.