2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/103783A construction is introduced for modifying hyperkaehler manifolds with tri-Hamiltonian circle action, that in favourable situations increases the second Betti number by one. This is based on the symplectic cut construction of Lerman. In 4 or 8 dimensions the construction may be interpreted as adding a D6-brane. A number of examples are given and generalisations to three-Sasaki and hypersymplectic geometry discussed.17 pagesDifferential GeometryHigh Energy Physics - Theory53C26; 53D20, 57S25, 57N65text