Jeff Dunn writes appreciatively of "Madam Butterfly" and its fertility
as an unacknowldged "source" for Broadway/West End musicals.

Puccini's score itself is indeed a delectable prismatic reflection
of Debussy, Wagner and even Massenet.  All these influences are well
documented, and better absorbed.  However, there's another which I haven't
seen mentioned anywhere - though it seems so obvious once you've made the
lateral jump that I expect someone somewhere has picked up on it.

Just listen to the fugato Prelude to Act One, then follow it up with
the fugato opening of "The Bartered Bride" overture.  Enough said, I think.
It might well be a conscious quote, as Smetana's title would do almost
equally well for the Puccini.

Christopher Webber,  Blackheath, London,  UK.
http://www.nashwan.demon.co.uk/zarzuela.htm
"ZARZUELA!"