Flow typing for passing Unstated Container as props?

file.js

// @flow
import React from "react";
import { render } from "react-dom";
import { Provider, Subscribe, Container } from "unstated";

type CounterState = {
  count: number
};

class CounterContainer extends Container<CounterState> {
  state = { count: 0 };

  increment() {
    this.setState({ count: this.state.count + 1 });
  }

  decrement() {
    this.setState({ count: this.state.count - 1 });
  }
}

function Counter(props: /* { counter: ??? } */) {
  const counter = props.counter;
  return (
    <div>
      <button onClick={() => counter.decrement()}>-</button>
      <span>{counter.state.count}</span>
      <button onClick={() => counter.increment()}>+</button>
    </div>
  );
}

// What's the type of props.counter? 
// Should CounterContainer export a CounterContainerType?
// Should the functions be on state?
// Something else??
//
type CounterContainerType = {
    state: CounterState,
    increment: () => void,
    decrement: () => void,
}
//

function ConnectedCounter() {
  <Subscribe to={[CounterContainer]}>
    {counter => <Counter counter={counter} />}
  </Subscribe>;
}

render(
  <Provider>
    <Counter />
  </Provider>,
  window.simple
);