In the math diagram of grade one, those circled with hueco mundo or crossed with diagonal lines all mean to be removed, and all are calculated by subtraction.

The dotted circle is used to indicate subtraction. Three diagonal lines mean putting things on with three sticks.

This dotted line is not the edge of the figure, but circled, and the previous numbers are crossed out with diagonal lines, so it should be explained that the numbers in the dotted line can only be found by subtracting the crossed out numbers. Maybe I wrote this understanding, or maybe it's another way of understanding.