Harmonic morphism
In mathematics, a harmonic morphism is a (smooth) map ϕ : ( M m , g ) → ( N n , h ) {\displaystyle \phi :(M^{m},g)\to (N^{n},h)} between Riemannian manifolds that pulls back real-valued harmonic functions on the codomain to harmonic functions on the domain. Harmonic morphisms form a special class of harmonic maps, namely those that are horizontally (weakly) conformal.