Misc: In a general sense, one who pleads for another in a court of law or other tribunal?

Questions

Why is the celebrated Chopin waltz nicknamed "Minute"?

Which composer wrote a concerto for three pianos and orchestra?

In listings of Mozart's works, the title is often followed bY a "K."and a number. What's the "K" stand for?

Who first published the admonition "please do not shoot the pianist.He is doing his best"?

What was the first name of Joplin, composer of "The Entertainer"and other rags?