operator: find-inverse

    description:
        find-inverse[op1, op2, ... , opn]
        learn the set of inverses for the given operator(s)       

    examples:
        load fred-sam-friends.sw
        find-inverse[friends]
        dump
            ----------------------------------------
             |context> => |context: friends>
            previous |context> => |context: global context>
            
            friends |Fred> => |Jack> + |Harry> + |Ed> + |Mary> + |Rob> + |Patrick> + |Emma> + |Charlie>
            friends |Sam> => |Charlie> + |George> + |Emma> + |Jack> + |Rober> + |Frank> + |Julie>
            
            inverse-friends |Jack> => |Fred> + |Sam>
            inverse-friends |Harry> => |Fred>
            inverse-friends |Ed> => |Fred>
            inverse-friends |Mary> => |Fred>
            inverse-friends |Rob> => |Fred>
            inverse-friends |Patrick> => |Fred>
            inverse-friends |Emma> => |Fred> + |Sam>
            inverse-friends |Charlie> => |Fred> + |Sam>
            inverse-friends |George> => |Sam>
            inverse-friends |Rober> => |Sam>
            inverse-friends |Frank> => |Sam>
            inverse-friends |Julie> => |Sam>
            ----------------------------------------
        
    see also:
        find-unique