His work is directly related to the universal logic project:
He was keynote speaker at the first UNILOG in Montreux in 2005.
Later I visited him at CUNY.
His main work is based on Paul Hertz's idea of Satzsysteme, from which the work of Gentzen is derived.
See: "A Structuralist Theory of Logic", Cambridge University Press, New York, 1992.
and the first chapter of: "Universal Logic: An Anthology, From Paul Hertz to Dov Gabbay"
JYB