Perpendicular bisectors of four sides of quadrangle

[Бк] , [Бй] , [^] , [Би]Perpendicular bisectors of four sides of quadrangle / Always parallelogram(GC World : Various Problems ,QuadrangleБиQuadrangle)

What can you say about quadrangle EFGH, when quadrangle ABCD is a parallelogram?

GC/Win

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