³⁶In more detail: For the second-order Taylor approximation in (70), we implicitly assume that the absolute value of the second-order term is much smaller than that of the ﬁrst-order one, i.e. $|ρ−1ℵ| ≥ |(ρ− 1)(ρ−1 − 1)(ℵ2∕2)|$ . Substituting (71), the above could be simpliﬁed to $1 ≥ (− þγ∕℧)ω$ , therefore we have $ˆþ < 0 γ$ . This simple justiﬁcation is based on the conﬁdence that we have proved above that RIC and GIC $Γ$ guarantee the denominator of the fraction in (67) is positive.