romana plots their escape by drawing ideas from her research into concepts of transversality as outlined in structural stability and morphogenesis ( ren thom , then of the ihes at bures-sur-yvette , 1972 ) , the work on chaos theory of christopher zeeman ( then of warwick university ) , her own developing thesis on number theory and non-euclidean geometry and the breakthrough book bifurcations on a rectilinear grid ( thomas lger , professor of mathematics at the university of jena , 1986 ) .