= Permutation diffeomorphisms of identical connected summands
For a connected sum of identical oriented manifolds of dimension at least three, one can permute the attachment balls in a punctured sphere and match the attached copies by their chosen parametrizations. This gives orientation-preserving diffeomorphisms realizing the permutations on the middle cohomology summands. For sums of complex projective planes, these permutations preserve the diagonal positive intersection form.
// Destination: geometry-and-topology.bigb
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