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An antiparallelogram or contraparallelogram[1] is a quadrilateral in which the pairs of nonadjacent sides are congruent, but in which two opposite sides intersect (unlike in a parallelogram) and are therefore not parallel. The antiparallelogram has been used as a form of four bar linkage, and in this context is also called a butterfly or bow-tie linkage. As a linkage, it has a point of instability in which it can be converted into a parallelogram and vice versa. For both the parallelogram and antiparallelogram linkages, if one of the long edges of the linkage is fixed as a base, the free joints move on equal circles, but in a parallelogram they move in the same direction with equal velocities while in the antiparallelogram they move in opposite directions with unequal velocities.[2] [edit] References
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