Hyper-Kähler geometry via dualization

We present a method of construction of sigma-models with target space geometries different from conformally flat ones. The method is based on treating the constancy of a coupling constant as a dynamical constraint following as an equation of motion. In this way we buildN=8 supersymmetric four-dimensional sigma-models ind=1 with hyper-Kähler target space possessing one isometry, which commutes with supersymmetry.