There is duality between monitors and message passing. What is that duality exactly?

In the table, the rows represent notions about monitors, and the columns represent notions about message passing.

Click the circle in a cell to represent that a notion about monitors is dual to a notion about message passing. You're only supposed to select one circle per row.

	`request` channel and operation kinds	arms of case statement on operation kind	retrieve and process pending request	`send request(); receive reply()`	save pending request	local server variables	`send reply()`	`receive request()`
procedure bodies	O	O	O	O	O	O	O	O
monitor entry	O	O	O	O	O	O	O	O
permanent variables	O	O	O	O	O	O	O	O
`wait`	O	O	O	O	O	O	O	O
procedure identifiers	O	O	O	O	O	O	O	O
`signal`	O	O	O	O	O	O	O	O
procedure call	O	O	O	O	O	O	O	O
procedure return	O	O	O	O	O	O	O	O