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HELP ISIN A. Sloman, July 1982 <pattern> isin <list> -> <boolean> ISIN is an infix operator which takes a pattern and a list and returns <true> or <false>. The result is true if at least one element of the list matches the pattern. As a side effect the element of the list which matched the pattern is assigned to the global variable IT. For example: vars x y; [?x isa ?y] isin [[colour a red] [colour b blue] [a isa block] [b isa block]] => ** <true> x=> ** a y=> ** block it=> ** [a isa block] See also HELP *AREIN - matches a list of patterns against list elements *MATCHESONEOF - matches a list against elements of a list of patterns *DATABASE - on use of the POP-11 DATABASE *PRESENT - matches a pattern against the DATABASE *FOREACH - selective iteration over a database *MATCHES - summary of the POP-11 matcher