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A search for the 4He − η bound state via exclusive measurement of the excitation function for the dd → 3Hepπ− reaction, was performed at the Cooler Synchrotron COSY-Jülich with the WASA-at-COSY detection system. The data were taken during a slow acceleration of the beam from 2.185GeV/c to 2.400GeV/c crossing the kinematic threshold for the η production in the dd → 4He η reaction at 2.336 GeV/c. The corresponding excess energy in the 4He − η system varied from −51.4 MeV to 22 MeV. The shape of the excitation function for the dd → 3Hepπ− was examined. No signal of the 4He − η bound state was observed in the excitation function.