uTake2 tt cons N uLength tt s length L and tt T T isNatIList isNatList isNat tt isNat isNat isNat isNatList isNatIList tt isNatIList and isNat isNatIList isNatList tt isNatList and isNat isNatList isNatList and isNat isNatIList zeros cons 0 take 0 IL uTake1 isNatIList uTake1 tt nil take s M cons N uTake2 and isNat and isNat isNatIList length cons N uLength and isNat isNatList 2.2 NaTT certifiable-1.6