⊦ firstn(n, a ' + x) = a ' + firstn(n - 1, x), n = 0
Used simplifier rules: sublist-def: ⊦ sublist(m, n, x) = firstn(n, restn(m, x));%restN-zero: ⊦ restn(0, x) = x;% ⊦ n -1 = n - 1; (s)