terms N cons recip sqr N terms s N sqr 0 0 sqr s X s add sqr X dbl X dbl 0 0 dbl s X s s dbl X add 0 X X add s X Y s add X Y first 0 X nil first s X cons Y Z cons Y first X Z half 0 0 half s 0 0 half s s X s half X half dbl X X 2.2 half s s X half X sqr s X sqr X terms N terms s N sqr s X dbl X sqr s X add sqr X dbl X add s X Y add X Y first s X cons Y Z first X Z terms N sqr N dbl s X dbl X true first s X cons Y Z first X Z true s 1 1 recip 1 0 dbl 1 0 dbl 1 0 terms 1 0 half 1 0 half 1 0 sqr 1 0 0 0 0 first 2 2 0 nil 0 0 first 2 0 cons 2 2 1 add 2 0 add 2 0 sqr 1 0 terms 1 0 terms N terms s N true Failed! NaTT certifiable-1.6