The symmetry structure of the heavenly equation
  We show that excitations of physical interest of the heavenly equation are generated by symmetry operators which yields two reduced equations with different characteristics. One equation is of the Liouville type and gives rise to gravitational instantons, including those found by Eguchi-Hanson and Gibbons-Hawking. The second equation appears for the first time in the theory of heavenly spaces and provides meron-like configurations endowed with a fractional topological charge. A link is also established between the heavenly equation and the socalled Schr{\"o}der equation, which plays a crucial role in the bootstrap model and in the renormalization theory. 
E. Alfinito, G. Soliani and L. Solombrino