Works in the public domain are those whose intellectual property rights have expired, have been forfeited, or are inapplicable. For example, the works of Shakespeare and Beethoven, most of the early silent films, the formulae of Newtonian physics, the Serpent encryption algorithm and powered flight are all now in the public domain. The term is not normally applied to situations where the creator of a work retains residual rights, in which case use of the work is referred to as "under license" or "with permission".