design
  cons module Register
    cons input d 1 nil
    cons state q 1 false
    cons next q d
    nil
    cons output value 1 q nil
  cons module Independent
    cons input a 1 cons input b 1 nil
    cons inst left Register cons a nil
    cons inst right Register cons b nil
    nil
    cons output first 1 at left value
    cons output second 1 at right value
    nil
  nil
  Independent
  cons test independent Independent
    cons tick cons true cons false nil cons false cons false nil
    cons tick cons false cons true nil cons true cons false nil
    cons tick cons false cons false nil cons false cons true nil
    nil
  nil