Miura Transformations for Integrable Evolution Equations of the Form   $u_t=u_{xxx}+f(t,x,u,u_x,u_{xx})$
  The paper is withdrawn due to an error in Section 3.2. The remaining of the results are included in the preprint solv-int/9605004. 
Ayse Humeyra Bilge and Fatma Ozdemir