Concentration (game) as an educational game. Any deck of playing cards may be used, although there are also commercial sets of cards with images. The rules given here are for a standard deck of 52 cards, which are normally laid face down in four rows of 13 cards each. The two jokers may be included for a total of six rows of nine cards each. Additional packs can be used for added interest. Standard rules need not be followed: the cards can be spread out anywhere, such as all around a room. In turn, each player chooses two cards and turns them
Pack (compression) Pack (compression) Pack is a (now deprecated) Unix shell compression program based on Huffman coding. The unpack utility will restore files to their original state after they have been compressed using the "pack" utility. If no files are specified, the standard input will be uncompressed to the standard output. Although obsolete, support for packed files exists in modern compression tools such as gzip and 7-zip. Files compressed by "pack" are typically given the extension ".z" (not to be confused with the ".Z" of compress). Files can be returned to their original state using "unpack". In addition, there may also be