["sequence", {}, [
  ["trace", { "first string": null }, []],
  ["trace", { "second string": null }, []],
  ["concurrence", {"count": 2}, [
    ["trace", { "when will this appear": null }, []],
    ["trace", { "who knows": null }, []],
    ["sequence", {}, [
      ["trace", { "third string": null }, []],
      ["trace", { "fourth string": null }, []]
    ]]
  ]],
  ["trace", { "final string": null }, []]
]]

["sequence", {}, [
  ["trace", { "first string": null }, []],
  ["trace", { "second string": null }, []],
  ["concurrence", {}, [
    ["trace", { "when will this appear": null }, []],
    ["trace", { "who knows": null }, []],
    ["sequence", {}, [
      ["trace", { "third string": null }, []],
      ["trace", { "fourth string": null }, []]
    ]]
  ]],
  ["trace", { "final string": null }, []]
]]

Remove unimplemented cruft from definition fixture
Remove unimplemented cruft from definition fixture