Re: question about transposing an interval of a 4th - Looks like I found the answer

[Chip]

I figured it out - without any special trickery or anything else.
My piece is arrange as follows, a very truncated version of an 8 horn piece -

\include ""
\version ""
\header {}
\paper {}
global = {\key g \major and more stuff }
\trumpetnotes1 = { a b c d e f g }
trptnotes1 = \relative c''' { \global << \trumpetnotes1 >> }
\trumpetnotes2 = { a b c d e f g }
trptnotes2 = \relative c''' { \global << \trumpetnotes2 >> }
\book { \score {
<< \new StaffGroup = "trumpets" << \new Staff = "trumpetnotes1" \trpt1
                                                           \new Staff = "trumpetnotes2" \trpt2 >> }
\book { \score { << \new Staff = "trpt1" \trpt1 >>}}
\book { \score { << \new Staff = "trpt2" \trpt2 >>}}
\layout { \context { \Score } }

For this example the above notes are entered in the transposing instrument key. This is for Bb Trumpet, the concert key is F, the Trumpet key is G. Both parts are entered the same, then this is placed in the section for the 2nd Trumpet -

 \transpose g d \relative c''' { \transpose d g << \trptnotes2>> }

Thus the above example now looks like this -

\include ""
\version ""
\header {}
\paper {}
global = {\key g \major and more stuff }
\trumpetnotes1 = { a b c d e f g }
trptnotes1 = \relative c''' { \global << \trumpetnotes1 >> }
\trumpetnotes2 = { a b c d e f g }
trptnotes2 =  \transpose g d \relative c''' { \transpose d g \global << \trptnotes2>> }
\book { \score {
<< \new StaffGroup = "trumpets" << \new Staff = "trumpetnotes1" \trpt1
                                                           \new Staff = "trumpetnotes2" \trpt2 >> }
\book { \score { << \new Staff = "trpt1" \trpt1 >>}}
\book { \score { << \new Staff = "trpt2" \trpt2 >>}}
\layout { \context { \Score } }

What happens is the original key is transposed from G to D (changing the key sig from one sharp to two sharps and dropping the written notes a fourth) before the first {, then inside the {} it is transposed again, this time from D to G (leaving the notes in the new position but changing the key sig back to one sharp).

I don't understand how or why this works but it does. And whether the interval is diatonic or harmonic, I don't know, but it gets the job done. Then I can just go in and fix very few individual notes as needed.
Regards,
Chip