On a problem of Sakai in unbounded derivations

Let A_θ be the irrational rotation algebra. Then there exist non approximately bounded pregenerators δ_i(i = 1, 2) of A_θ with the same domain such that given a ¹-derivation δ of A_θ with D(δ) = D(δ_i), there exist (k,l)∈$\text{R}$² and an approximately bounded ¹-derivation δ₃of A_θ such that δ = kδ₁ + lδ₂ + δ₃, which can be considered as a solution of a problem of Sakai for two dimensional space quantizations.