Superconductivity in the lanthanum lanthanide barium strontium copper oxide $((La,Ln)2-x(Ba,Sr)xCuO_4)$.

Several $(La1-yLny)2-xSrx(Bax)CuO_4$ systems show supercond. in the 15-40 K region. Marginal metalicity of the non-superconducting phases and the role of the nominal $Cu^3^+/Cu^2^+$ ratio are discussed. The possible importance of hole-hole coupling (forming resonating O-O bonds) is indicated.