on- strating by adequate evidence that there has been a substantial breach by defend- ant); State v. Rivest 106 Wis.2d 406, 316 N.W.2d 395, 398-99 (Wis.1982) (adopting a beyond a reasonable doubt standard); United States v. Skalsky, 616 F.Supp. 676, 681 (D.N.J.I985) (requiring proof of ma- terial breac