4log2(u)-3 >= log²2(u)
log²2(u)-4log2(u)+3 <= 0</p>
log2(u) = t
t²-4t+3 <= 0</p>
t²-t-3t+3 <= 0</p>
t(t-1)-3(t-1) <= 0</p>
(t-1)(t-3) <= 0</p>
+. -. +
------[1]------[3]------
1 <= t <= 3</p>
1 <= log2(u) <= 3</p>
2¹ <= 2^log2(u) <= 2³</p>
2 <= u <= 8</p>
u€[2; 8]