The Fission Theory: This theory proposes that the Moon was once part of the Earth and somehow separated from the Earth early in the history of the solar system.
This provides modular approach to programming. Classes. A class is a concept used in object oriented programming languages such as C++, PHP, and JAVA etc. Apart from holding data, a class is also used to hold functions. An object is an instant of a class. In case of variables, the type is the class whereas the variable is the object.
Difference between a class and a set. I know what a set is. I have no idea what a class is. As best as I can make out, every set is also a class, but a class can be larger than any set. This obviously makes no sense whatsoever, since sets are of unlimited size.