A JTE finally came back to me to comment on the maths I've been using to correct students essays. She informed me she got it, and that the students managed to work out what it meant. The math/science stream ones had the upper hand in this, while the humanities ones were left confused. Fortunately, the students helped each other to understand. Unfortunately for humankind, and Japan in particular, the teacher also pointed out that the girls in the class had particular difficulty in understanding, but that they boys helped them.
Because obviously, girls are so woeful at maths.