Remark on Callias' index theorem (Q1178348)

The author considers the Dirac operator \(L\) in \(\mathbb{R}^ 2\). The \(L^ 2\)-index of \(L\) is given by a general result of Hörmander-Fedosov. On the other hand that operator was originally studied by \textit{C. Callias} [Commun. Math. Phys. 62, 213-234 (1978; Zbl 0416.58024)] who obtained a simpler index formula. Following a topological approach of \textit{R. Bott} and \textit{R. Seeley} [Commun. Math. Phys. 62, 235-245 (1978; Zbl 0409.58019)] the author precisely derives the index formula of Callias from the Hörmander-Fedosov index theorem.