transposed parts3

[David Bobroff]

>%%part-clarinet.ly
>\include "parts.ly"
>\score { \ontext Staff=clarpart {
>  \transpose ees {
>    \clarinet}
>}}

I've tried a few variants on this theme.  I get 

error: parse error, unexpected STRING, expecting PITCH or NOTENAME_PITCH or
TONICNAME_PITCH:

In my music file I'm using \relative c' in one part, for example.  Will the
specification of a pitch value at this point negate my \transpose value?
According to the docs both can be used as long as \transpose comes first.
Experimentation shows that \relative will not work without a pitch reference.

Help?

-David