“…This approach gives both finite action solutions (instantons) and infinite action solutions (such as nonlinear plane waves). The solutions obtained are written in terms of quasideterminants (Gelfand and Retakh (1991); Gelfand and Retakh (1992)) which appear also in the construction of exact soliton solutions in lower-dimensional noncommutative integrable equations such as the Toda equation (Etingof, Gelfand and Retakh (1997); Etingof, Gelfand and Retakh (1998); Li and Nimmo (2008); ), the KP and KdV equations (Dimakis and Müller-Hoissen (2007); Etingof, Gelfand and Retakh (1997); ; Hamanaka (2007)), the Hirota-Miwa equation (Gilson, Nimmo and Ohta (2007); Li, Nimmo and Tamizhmani (2009);Nimmo (2006)), the mKP equation (Gilson, Nimmo and Sooman (2008a); Gilson, Nimmo and Sooman (2008b)), the Schrödinger equation (Goncharenko and Veselov (1998); Samsonov and Pecheritsin (2004)), the Davey-Stewartson equation (Gilson and Macfarlane (2009)), the dispersionless equation (Hassan (2009)), and the chiral model (Haider and Hassan (2008)), where they play the role that determinants do in the corresponding commutative integrable systems. We also clarify the origin of the results from the viewpoint of noncommutative twistor theory by using noncommutative Penrose-Ward correspondence or by solving a noncommutative Riemann-Hilbert problem.…”