/x - 1\ atan|-----| \ 2 /
atan((x - 1)/2)
1 ---------------- / 2\ | (x - 1) | 2*|1 + --------| \ 4 /
-(-1 + x) ------------------ 2 / 2\ | (-1 + x) | 4*|1 + ---------| \ 4 /
/ 2 \ | 4*(-1 + x) | 4*|-1 + -------------| | 2| \ 4 + (-1 + x) / ---------------------- 2 / 2\ \4 + (-1 + x) /