polyphonic shorthand; line-spanner-interface in Hairpin

[Kieren MacMillan]

Hello,

Thanks to Carl's patient help, I've successfully submitted my first  
patch as a Frog!
<insert sound of trumpets, throw confetti, etc.>

1. For my next task, I was thinking of fixing the polyphonic  
shorthand. Unfortunately, searching the tree for
  <<
gives a couple of thousand hits...  ;-)
Any hints on where that shorthand is defined would be greatly  
appreciated.

2. Can Hairpin inherit line-spanner-interface? If so, can this be  
done in Scheme, or does it require C++?

Thanks,
Kieren.