active zeros mark cons 0 zeros active U11 tt L mark s length L active U21 tt mark nil active U31 tt IL M N mark cons N take M IL active and tt X mark X active isNat 0 mark tt active isNat length V1 mark isNatList V1 active isNat s V1 mark isNat V1 active isNatIList V mark isNatList V active isNatIList zeros mark tt active isNatIList cons V1 V2 mark and isNat V1 isNatIList V2 active isNatList nil mark tt active isNatList cons V1 V2 mark and isNat V1 isNatList V2 active isNatList take V1 V2 mark and isNat V1 isNatIList V2 active length nil mark 0 active length cons N L mark U11 and isNatList L isNat N L active take 0 IL mark U21 isNatIList IL active take s M cons N IL mark U31 and isNatIList IL and isNat M isNat N IL M N active cons X1 X2 cons active X1 X2 active U11 X1 X2 U11 active X1 X2 active s X s active X active length X length active X active U21 X U21 active X active U31 X1 X2 X3 X4 U31 active X1 X2 X3 X4 active take X1 X2 take active X1 X2 active take X1 X2 take X1 active X2 active and X1 X2 and active X1 X2 cons mark X1 X2 mark cons X1 X2 U11 mark X1 X2 mark U11 X1 X2 s mark X mark s X length mark X mark length X U21 mark X mark U21 X U31 mark X1 X2 X3 X4 mark U31 X1 X2 X3 X4 take mark X1 X2 mark take X1 X2 take X1 mark X2 mark take X1 X2 and mark X1 X2 mark and X1 X2 proper zeros ok zeros proper cons X1 X2 cons proper X1 proper X2 proper 0 ok 0 proper U11 X1 X2 U11 proper X1 proper X2 proper tt ok tt proper s X s proper X proper length X length proper X proper U21 X U21 proper X proper nil ok nil proper U31 X1 X2 X3 X4 U31 proper X1 proper X2 proper X3 proper X4 proper take X1 X2 take proper X1 proper X2 proper and X1 X2 and proper X1 proper X2 proper isNat X isNat proper X proper isNatList X isNatList proper X proper isNatIList X isNatIList proper X cons ok X1 ok X2 ok cons X1 X2 U11 ok X1 ok X2 ok U11 X1 X2 s ok X ok s X length ok X ok length X U21 ok X ok U21 X U31 ok X1 ok X2 ok X3 ok X4 ok U31 X1 X2 X3 X4 take ok X1 ok X2 ok take X1 X2 and ok X1 ok X2 ok and X1 X2 isNat ok X ok isNat X isNatList ok X ok isNatList X isNatIList ok X ok isNatIList X top mark X top proper X top ok X top active X 2.2 active U11 tt L length L active length cons N L isNatList L active U21 X U21 active X proper U11 X1 X2 proper X1 active isNatList cons V1 V2 isNatList V2 active s X active X active length X length active X U21 ok X U21 X active U31 X1 X2 X3 X4 active X1 active take s M cons N IL U31 and isNatIList IL and isNat M isNat N IL M N active U31 X1 X2 X3 X4 U31 active X1 X2 X3 X4 active isNatIList cons V1 V2 and isNat V1 isNatIList V2 active take s M cons N IL isNat M active take s M cons N IL isNatIList IL active U31 tt IL M N cons N take M IL active take 0 IL isNatIList IL active isNatList take V1 V2 and isNat V1 isNatIList V2 proper isNat X isNat proper X isNat ok X isNat X active isNatList take V1 V2 isNat V1 active cons X1 X2 cons active X1 X2 U21 mark X U21 X active U11 X1 X2 active X1 top ok X active X active isNatIList cons V1 V2 isNat V1 take X1 mark X2 take X1 X2 active isNat length V1 isNatList V1 active take X1 X2 take active X1 X2 active length X active X U31 ok X1 ok X2 ok X3 ok X4 U31 X1 X2 X3 X4 active isNat s V1 isNat V1 s mark X s X proper s X proper X proper U31 X1 X2 X3 X4 proper X2 proper U31 X1 X2 X3 X4 proper X4 active take s M cons N IL and isNat M isNat N active U11 X1 X2 U11 active X1 X2 active cons X1 X2 active X1 proper isNatList X proper X proper cons X1 X2 proper X1 active and X1 X2 active X1 proper cons X1 X2 cons proper X1 proper X2 and mark X1 X2 and X1 X2 top mark X proper X length mark X length X active take s M cons N IL and isNatIList IL and isNat M isNat N active and X1 X2 and active X1 X2 proper s X s proper X proper isNatIList X isNatIList proper X active take X1 X2 take X1 active X2 active take X1 X2 active X1 s ok X s X active s X s active X proper take X1 X2 take proper X1 proper X2 U31 mark X1 X2 X3 X4 U31 X1 X2 X3 X4 proper U11 X1 X2 proper X2 cons ok X1 ok X2 cons X1 X2 active isNatList take V1 V2 isNatIList V2 proper cons X1 X2 proper X2 proper and X1 X2 proper X2 active zeros cons 0 zeros proper U31 X1 X2 X3 X4 U31 proper X1 proper X2 proper X3 proper X4 active isNatIList cons V1 V2 isNatIList V2 proper U31 X1 X2 X3 X4 proper X3 active U31 tt IL M N take M IL proper isNatList X isNatList proper X proper U21 X proper X active isNatList cons V1 V2 and isNat V1 isNatList V2 active take 0 IL U21 isNatIList IL U11 mark X1 X2 U11 X1 X2 active U21 X active X cons mark X1 X2 cons X1 X2 proper U11 X1 X2 U11 proper X1 proper X2 isNatList ok X isNatList X active isNatList cons V1 V2 isNat V1 active length cons N L U11 and isNatList L isNat N L active length cons N L isNat N length ok X length X top ok X top active X U11 ok X1 ok X2 U11 X1 X2 proper isNatIList X proper X proper and X1 X2 proper X1 proper U21 X U21 proper X and ok X1 ok X2 and X1 X2 active take s M cons N IL isNat N active length cons N L and isNatList L isNat N take mark X1 X2 take X1 X2 active isNatIList V isNatList V take ok X1 ok X2 take X1 X2 proper take X1 X2 proper X2 proper length X length proper X top mark X top proper X active U11 tt L s length L proper isNat X proper X proper U31 X1 X2 X3 X4 proper X1 proper take X1 X2 proper X1 proper length X proper X active take X1 X2 active X2 isNatIList ok X isNatIList X proper and X1 X2 and proper X1 proper X2 true top mark X top proper X top ok X top active X true Failed! NaTT certifiable-1.6