Ozone layer upper-atmosphere ozone-depletion rate slowed down significantly during the previous decade. Some breakdown can be expected to continue because of ODSs used by nations which have not banned them, and because of gases which are already in the stratosphere. Some ODSs, including CFCs, have very long atmospheric lifetimes, ranging from 50 to over 100 years. It has been estimated that the ozone layer will recover to 1980 levels near the middle of the 21st century. A gradual trend toward "healing" was reported in 2016. Compounds containing C–H bonds (such as hydrochlorofluorocarbons, or HCFCs) have been designed to replace CFCs in certain
Layer by Layer there are many variant techniques for the final layer, depending on whether the corner or edge pieces are solved first. The CFOP speedcubing technique, developed by Jessica Fridrich and others in the 1980s, similarly divides the puzzle into layers to be solved. However the method uses far more algorithms and shortcuts than the beginners' methods. Layer by Layer The Layer by Layer method is a method of solving the 3x3x3 Rubik's Cube. Many beginners' methods use this approach, but it also forms the basis of the CFOP speedcubing technique. The Layer by Layer Method was pioneered by David Singmaster in