How to abbreviate Pen Down?

The ways to abbreviate Pen Down.

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Pen Down
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APASmart Define. (2014). Pen Down. Retrieved July 31, 2014, from http://smartdefine.org/pen_down/abbreviations/a
ChicagoSmart Define. 2014. "Pen Down" http://smartdefine.org/pen_down/abbreviations/a (accessed July 31, 2014).
HarvardSmart Define 2014, Pen Down, Smart Define, viewed 31 July, 2014, <http://smartdefine.org/pen_down/abbreviations/a>.
MLASmart Define. "Pen Down" 9 June 2014. Web. 31 July 2014. <http://smartdefine.org/pen_down/abbreviations/a>