Solution::
(*i | 0<i≤2m ∧ even.i : i) = < (8.22), with x,y,f.j := i,j,2j > (*j | (0<i≤2m ∧ even.i)[i:=2j] : i[i:=2j]) = < textual substitution > (*j | 0<2j≤2m ∧ even(2j) : 2j) = < even(2j) ≡ true, (3.39) > (*j | 0<2j≤2m : 2j) = < 0<2j≤2m ≡ 0<j≤m > (*j | 0<j≤m : 2j) = < (8.21), x,y := j,i > (*i | 0<i≤m : 2i)
(*i | -8<i≤0 : f.i) = < 8.22, with x,y,f.j := i,j,-j > (*j | -8<-j≤0 : f.(-j)) = < rewrite range (using a<b ≡ -a>-b) > (*j | 0≤j<8 : f(-j))