An add-on (more commonly add-on method) is a method or substeps used in conjunction with a principal method. It is the opposite of a stand-alone method. An add-on is used instead of the principal method or steps depending on the case encountered. This allows solvers using an add-on method to take better advantage of the particular case presented.


Many experimental substeps or groups of substeps were proposed from the outset as an add-on to a more mainstream method. These include:

Some methods or variations were originally proposed as stand-alone methods but are more frequently used as an add-on. These include: