operator: less-than

    description:
        less-than[value] ket
        returns the ket if value < the value in ket
        otherwise, return |>
        ie, a value filter

    examples:
        less-than[5] |7>
            |>

        less-than[3] |price: 3.50>
            |>

        less-than[26] |number: 25>
            |number: 25>

        -- if the ket has no float value, then return |>
        less-than[13] |the cat>
            |>

    see also:
        greater-than, greater-equal-than, less-equal-than, equal, in-range
        is-greater-than, is-greater-equal-than, is-less-than, is-less-equal-than, is-equal, is-in-range