In SuperMemo, subsets are sets of elements. Subsets are usually viewed in the browser. Subsets are processed with subset operations. Subsets can be stored in subset files for later use. The default extension of subset files is sub. Each element in a subset file is stored as a four-byte element number. This way, subset file size in bytes is four times the number of elements in the subset. The same subset files can be used by different collections, but such use is meaningful only if the collections have the same numbering of elements (e.g. if these are copies of the same collection).
To create a subset file use one of the following options:
Some subset files are created automatically for you. You can view them with View : Subset. For example: last_browser (subset with all elements displayed in the last opened browser), searched (subset with all elements found with the last Ctrl+F search), last_child (subset with elements extracted with the last Child operation in the browser), tasklist (subset will all tasks extracted with Tools : Open in browser on the tasklist manager menu), etc.
Subset can be processed using a nearly infinite combination of options and commands in SuperMemo. Here are only a few examples: