(header ((client) hello_modeling_nondet provides) ((sut) hello_modeling_nondet interface))
<external>.hello -> ...
... -> sut.hello
... <- sut.return
<external>.return <- ...
(trail "hello" "return")
... <- sut.world
<external>.world <- ...
(trail "world")
(labels "hello" "inevitable" "optional")
(eligible "inevitable" "optional")
