Re: Determining whether a pipeline has a (defaulted) output

>   For the purposes of output defaulting

"Output defaulting" is not defined and is not entirely clear.  Say
something more explicit such as "determining whether a subpipeline
with no declared outputs has an implicit primary output".

>    1) It is an atomic step whose step type definition specifies a
>       primary output port;
>    2) It is a named pipeline whose definition includes an explicit
>       primary output port;
>    3) It is a p:choose one of whose branches has a *last step* with a
>       primary output port;
>    4) It is a p:try whose p:group has a *last step* with a primary
>       output port;
>    5) It is some other compound step whose *last step* has a primary
>       output port;

Perhaps it would be better to define "last atomic step" and then say
"a last atomic step that is a named pipeline is considered to have a
primary output only if its definition explicitly includes one".

We need a similar rule for p:pipeline inputs.

Is this definition also used when checking compatibility of choose and
try branches?

-- Richard