A person taking a key deposit so a prospective tenant can inspect the premises gives a signed receipt at the time (receiver, payer, premises, date, amount, that it is a key deposit, when the key must be returned) and refunds the deposit in full when the key comes back, whether or not the person rents the premises.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.