On the Fredholm Property of Bisingular Pseudodifferential Operators

For operators belonging either to a class of global bisingular pseudodifferential operators on $\mathbb{R}^m \times \mathbb{R}^n$ or to a class of bisingular pseudodifferential operators on a product $M \times N$ of two closed smooth manifolds, we show the equivalence of their ellipticity (defined by the invertibility of certain operator-valued, homogeneous principal symbols) and their Fredholm mapping property in associated scales of Sobolev spaces. We also prove the spectral invariance of these operator classes and then extend these results to larger classes of Toeplitz type operators.