Thanks mate. Actually, even though it’s a contemporary poem about 50s jazz, the form is quite ancient. The ruba’i is a Persian form of the quatrain. (Multiple stanzas in the ruba’i form are a rubaiyat, like The Rubaiyat of Omar Khayyam.) Basically, a ruba’i is a four-line stanza, with a rhyme scheme of AABA and has been often used in English such as Robert Frost’s famous poem Stopping By Woods on a Snowy Evening. I’m sure this is much more than you ever wanted to know about the ruba’i!