operator: find-topic

    description:
        find-topic[op] |x>
        find most similar frequency list, defined with respect to op, of |x>
        the back-end to this operator uses normed-frequency-class

    examples:
        -- load some knowledge:
        -- in this case US census frequency list of male, female and last names:
        -- NB: unfortunately this is super memory hungry!
        web-load http://semantic-db.org/sw-examples/names.sw
        
        -- define our operator:
        guess-name-type |*> #=> find-topic[names] to-lower |_self>
        
        -- ask about 'Emma'
        guess-name-type |Emma>
            90.323|female name> + 9.677|last name>
        
        -- ask about 'Gina'
        guess-name-type |Gina>
            100|female name>
                    
        -- ask about 'Mark'
        guess-name-type |Mark>
            54.664|male name> + 28.633|last name> + 16.703|female name>

        -- ask about 'Fred'
        guess-name-type |Fred>
            63.294|male name> + 28.418|last name> + 8.288|female name>
        
        -- ask about 'Branson'
        guess-name-type |Branson>
            100|last name>

        -- define our guess-gender operator:
        name-type |male name> => |male>
        name-type |female name> => |female>
        guess-gender |*> #=> clean select[1,1] name-type find-topic[names] to-lower |_self>
        
        guess-gender |Lisa>
            |female>

        guess-gender |Eric>
            |male>

        guess-gender |Jane>
            |female>

        guess-gender |Stephen>
            |male>

    see also:
        similar-input, normed-frequency-class