The Gakhov Barriers and Extremals for the Level Lines
The regular Gakhov class G <sub>1</sub> consists of all holomorphic and locally univalent functions f in the unit disk with only one root of the Gakhov equation, which is the maximum of the hyperbolic derivative (conformal radius) of the function f . For the classes H defined by the conditions of Nehari and Becker’s type, as well as by some other inequalities, we have solved the problem of calculation of the Gakhov barrier, i.e., the value ρ( H ) = sup{ r ≥ 0: H<sub>r</sub> є G <sub>1</sub>}, where H<sub>r</sub> = { f<sub>r</sub> : f є H }, 0 ≤ r ≤ 1, and of an effective description of the Gakhov extremal, i.e., the set of f’ s in H with the level sets f<sub>r</sub> leaving G <sub>1</sub> when r passes through ρ( H ). Both possible variants of bifurcation, which provide an exit out of G <sub>1</sub> along the level lines, are represented.