1: What are the mathematical model that he is rejecting?
Geometry, Cartesian order of model, figure/ground contextualism

2: What is he replacing?
Topology, the event based interactive way of capturing space such as the catastrophe theory

3: and why?
Because architecture can no longer be bound by the static conditions of space and place. Traditional architectural theory which focuses on figure/ground contextualism has largely ignored the idea of the event. Now it is time to face with the problem of the event which the catastrophe theory can deal with.