; Step with alternating feet, left before right
(relation left (i64))
(relation right (i64))

(left 0)
(right 0)

(ruleset step-left)
(rule ((left x) (right x))
      ((left (+ x 1)))
      :ruleset step-left)

(ruleset step-right)
(rule ((left x) (right y) (= x (+ y 1)))
      ((right x))
      :ruleset step-right)

(run-schedule
      (repeat 10
            (saturate step-right)
            (saturate step-left)))

; We took 10 steps with the left, but the right couldn't go the first round,
; so we took only 9 steps with the right.
(check (left 10))
(check (right 9))
(fail (check (left 11)))
(fail (check (right 10)))