發送短信 : Levin's comparison theorems for nonlinear second order differential equations

__    __    _____      _____     ___              
\ \\ / //  |  ___||   / ___//   / _ \\      ___   
 \ \/ //   | ||__     \___ \\  / //\ \\    /   || 
  \  //    | ||__     /    // |  ___  ||  | [] || 
   \//     |_____||  /____//  |_||  |_||   \__ || 
    `      `-----`  `-----`   `-`   `-`     -|_|| 
                                             `-`