Hi Sminky,
The Lyrics of the Auld Triangle were copyrighted by Brendan Behan and Theatre Workshop in 1956 Fact
Dominic Behan published a songbook containing 100 songs called "The Singing Irish in 1967, mostly self-penned. Fact
Dominic published another songbook in 1973, called "Ireland Sings", containing another 100 songs. Fact
The Auld Triangle does not appear in either book. Fact
Bert Jansch, on his 2006 CD "The Black Swan" credits the song to Brendan Behan. Fact.
Facts are facts, talk is cheap.
Both Dicky and Brendan could not have envisaged how popular the song would become, or they may have made a better arrangement, Brendan being more interested in the Play than the song.