Abacus

an abacus drawn in single strokes: where the pointer sits along the rod splits the ten beads, the ones to its left packed against the left post and counted, the rest against the right.

key insight: one pointer position always gives one arrangement, since the split is read against the rod, which never moves, and never against a bead. the beads cannot pass each other, so the bead at the front of each moving group leaves first.

built on the hairline engine by lucas markes.