There was a column directly in my line of sight, so I could only see half the stage.

The answer, in the magazine’s Franz Kafka’s Garage column, is: “Long ago, half-ton pickups could haul half a ton.” But competition led to more capable trucks, though the name did not change.

In figure 1, you will find a column displaying a solid circle, a half-solid circle, and an empty circle for each received message.