Spinors on singular spaces and the topology of causal fermion systems

We propose causal fermion systems and Riemannian fermion systems as a framework for describing spinors on singular spaces. The underlying topological structures are introduced and analyzed. The connection to the spin condition in differential topology is worked out. The constructions are illustrated by many simple examples like the Euclidean plane, the two-dimensional Minkowski space, a conical singularity, a lattice system as well as the curvature singularity of the Schwarzschild space-time.