A book like this cannot define the logical symbols precisely, both because they may have somewhat different definitions in different logical systems, and because the methods of definition used by logicians cannot be explained in a few words. The following list merely offers rough equivalents in English for symbols and letters that are used in the Companion, with a few comments. For a more generous list of some of the alternatives see the entry ‘notations, logical’. And do note that any explanation given within a particular article overrides what is said here.
From The Oxford Companion to Philosophy in Oxford Reference.