ket fn: floor

floor:
    description:
        floor ket
        take the floor function of the value in the ket label
        while preserving the ket label category
        if the value is not a number, then return the ket unchanged
        also, we preserve the ket coefficient

    examples:
        -- floor of a simple number:
        floor |2.7>
            |2>

        -- floor of a number with a category, in this case "number"
        floor |number: 5.3>
            |number: 5>

        -- attempted floor of a non number:
        floor |alpha>
            |alpha>

    see also:
        ceiling, log