Scalar curvature and connected sums of self-dual 4-manifolds (Q550556)

\textit{S. Donaldson} and \textit{R. Friedman} proved that the connected sum of two self-dual Riemannian 4-manifolds can be again self-dual [Nonlinearity 2, No. 2, 197--239 (1989; Zbl 0671.53029)]. It is proved that this result can be extended to the positive scalar curvature case -- an analogue of the theorem of Gromov-Lawson and Schoen-Yau [\textit{M. Gromov} and \textit{H. B. Lawson jun.}, Ann. Math. (2) 111, 423--434 (1980; Zbl 0463.53025); \textit{R. Schoen} and \textit{S.-T. Yau}, Manuscr. Math. 28, 159--183 (1979; Zbl 0423.53032)]. The proof is based on twistor theory.