function Component(props) {
  // a and b are technically independent, but their mutation is interleaved
  // so they are grouped in a single reactive scope. a does not have any
  // reactive inputs, but b does. therefore, we have to treat a as reactive,
  // since it will be recreated based on a reactive input.
  const a = {};
  const b = [];
  b.push(props.b);
  a.a = null;

  // because a may recreate when b does, it becomes reactive. we have to recreate
  // c if a changes.
  const c = [a];

  // Example usage that could fail if we didn't treat a as reactive:
  //  const [c, a] = Component({b: ...});
  //  assert(c[0] === a);
  return [c, a];
}