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.

Match the columns in a cell to represent that a notion about monitors is dual to a notion about message passing.

	`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
monitor entry
permanent variables
`wait`
procedure identifiers
`signal`
procedure call
procedure return