Bill: question about cross-reference expansion

Title: 
Trust Framework Provider Adoption Process (TFPAP) - Version 1.0.1
Bill, I was thinking about how this would work to "fully expand" all XDI addresses into "$ statements", i.e., into XDI statements consisting of all $words (plus the four GCS symbols and literals).

It's a cool idea, and for a one-segment statement like +a, it's easy.

+a

(+/a)

+/$has/a

It is also easy for (+a).

(+a)

$$/$has//+a

$$/$has//(+/a)

$$/$has//+/$has/a

But I got stuck trying to expand the statement +a+b. 

+a+b

(+a/+b)

+a/$has/+b

(+/a)/$has/(+/b)

(+/$has/a)/$has/(+/$has/b)

At this point I don't know how to get rid of the parentheses and still make it a valid XDI statement.

Ideas?

=Drummond