Agility does not mean that:
    Problem solving must occur in two week
        increments
    You only talk informally about code 'smells'
        instead of having in-depth design
        discussions and review
    You equate refactoring code with good
        design (and don't design before you code)
    You do whatever works without regard to any
        process. Formal = bad; Informal = good
    Design descriptions and documentation add
        no value

    -- Rebecca Wirfs-Brock "Skills for the Agile Designer" (2002)
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fact = Hash.new {|h,n| n < 2 ? h[n] = 1 : h[n] = h[n-1] * n}
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This scratch is volatile --- here today, gone tomorrow (or sooner, or later).