Jérôme Durand-Lose. Abstract geometrical computation 4: small Turing universal signal machines. In Turlough Neary, Damien Woods, Anthony Karel Seda, Niall Murphy, editors, Complexity of Simple Programs 2008, CSP 2008, Cork, Ireland, December 6-7, 2008. Proceedings. pages 89-102, Cork University Press, 2008.