midi with multiple scores

[Jean-marc LEGRAND]

Hi list.

Working on lily 2.4 win XP.

I have a full score splitted like this :

\include "bI0X.ly"
\include "bII0X.ly"
\include "bc0X.ly"

\score      {
      <<
      \context Staff ="basseI" \basseI
      \context Staff ="basseII" \basseII
      \context Staff ="bassec" \bc
            >>
      \layout {textheight= 30.0 \cm
            interscoreline = 19 \pt}
      \midi {\tempo 4=100}
      }

with X going from 1 to 4.

So I have 4 score blocks, and 4 midi block.

When I run lily, I only get one midi file, corresponding to the last score 
block.

How can I get a full midi file, or at least 4 midi files ?

Regards.