What geometry theorem is dynamically being illustrated in the applet below? [br](Feel free to move the [b][color=#666666]gray points[/color][/b] anywhere you'd like.)
[b]Theorem:[/b][br][br]If parallel lines cut off congruent segments on one transversal, then they [color=#9900ff][b]cut off congruent segments on EVERY TRANSVERSAL[/b][/color].