A surface $Y$ that is in Peterson correspondence with a given surface $X$ and is, moreover, such that the asymptotic net on $Y$ corresponds to a conjugate net $\sigma$ on $X$ with equal invariants, and vice versa. The adjoint surface $Y$ is the rotation indicatrix for $X$, and vice versa. If $\sigma$ is a principal base for a deformation of $X$, then $Y$ is a Bianchi surface.
Adjoint surface. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Adjoint_surface&oldid=38634