Singular fibers And 4-dimensional cobordism group

Using the technique of singular fibers of C^∞ stable maps, we give a new proof to the theorem, originally due to Rohlin, that the oriented cobordism group of 4-dimensional manifolds is infinite cyclic and is generated by the cobordism class of the complex projective plane. A byproduct is a new and transparent proof of the signature formula, originally due to T. Yamamoto and the author, for 4-dimensional manifolds in terms of singular fibers.