Expense #9185 to ReactiveUI

Expenses are a way of getting reimbursed for things that we've already agreed to spend.

| Expense type​ | Audience | Approval Process | | ------------------|:----------:|------------:|---------:| | Stickers & postage | Rewards for backers | via OpenCollective > New Expense | | ReactiveUI book | Growing learning team | via OpenCollective > New Expense | | Anything else | | Consent via http://github.com/reactiveui/rfcs |

We recommend you seek pre-approval by opening a discussion over at http://github.com/reactiveui/rfcs before making any purchases. Expense claims are approved on a case-by-case basis by Geoffrey Huntley on behalf of the core team. When you raise an expense claim your name, expense claim reason and amount are automatically shared in our Slack community.