In mathematics, the hyperkähler quotient of a hyperkähler manifold acted on by a Lie group G is the quotient of a fiber of a hyperkähler moment map M → g ⊗ R 3 {\displaystyle M\to {\mathfrak {g}}\otimes \mathbb {R} ^{3}} over a G-fixed point by the action of G. It was introduced by Nigel Hitchin, Anders Karlhede, Ulf Lindström, and Martin Roček in 1987. Wikipedia