The text editing environment in Emacs uses a double space following a period to identify the end of sentences unambiguously ; the double space convention prevents confusion with periods within sentences that signify abbreviations . How Emacs recognizes the end of a sentence is controlled by the settings sentence @-@ end @-@ double @-@ space and sentence @-@ end . The vi editor also follows this convention ; thus , it is relatively easy to manipulate ( jump over , copy , delete ) whole sentences in both emacs and vi .