How would you describe (put into words) the theorem that's dynamically being illustrated below? [br](Feel free to move any of the larger points anywhere you'd like.)
In this illustration, [color=#ff00ff][b][i]AB[/i] is a chord[/b][/color] and the white point (let's call it [i]W[/i]) bisects the [color=#ff00ff][b]pink arc [i]AB[/i][/b][/color]. [color=#1e84cc][b]Point [i]N[/i] is any point on the blue arc [i]AB[/i][/b][/color]. Suppose tangent lines [i]l, k, [/i]and [i]p[/i] are drawn to the circle at points[i][color=#1e84cc][b]N[/b][/color], [color=#ff00ff][b]A[/b][/color], [/i]and [i]B[/i], respectively. Let [i]D[/i] = intersection of [i]l[/i] and [i]k[/i]. Let [i]E[/i] = intersection of [i]l[/i] and [i]p[/i]. Let [i]P[/i] = point where segment [i]DW[/i] intersects [i][color=#ff00ff][b]AB[/b][/color][/i] and let [i]Q[/i] = point where segment [i]EW[/i] intersects [i][color=#ff00ff][b]AB[/b][/color][/i]. Then [math]AP+BQ=PQ[/math][i][br][br]([/i][url=https://twitter.com/CutTheKnotMath]Alexander Bogomolny[/url] ([url=http://www.cut-the-knot.org/]Cut-the-Knot.org[/url]) illustrates it within [url=https://twitter.com/CutTheKnotMath/status/781586423610769409]this tweet[/url].) [br]