compound ket fn: is-less-equal-than

is-less-equal-than:
    description:
        is-less-equal-than[value] ket
        returns yes/no if the value in ket <= value

    examples:
        is-less-equal-than[80] |age: 76>
            |yes>

        is-less-equal-than[2010] |year: 2010>
            |yes>

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

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