Given a compact and connected four dimensional smooth Riemannian manifold (M,g0)\documentclass[12pt]{minimal}
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\begin{document}$$(M,g_0)$$\end{document} with kP:=∫MQg0dVg0<0\documentclass[12pt]{minimal}
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\begin{document}$$k_P := \int _M Q_{g_0} dV_{g_0} <0$$\end{document} and a smooth non-constant function f0\documentclass[12pt]{minimal}
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\begin{document}$$f_0$$\end{document} with maxp∈Mf0(p)=0\documentclass[12pt]{minimal}
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\begin{document}$$\max _{p\in M}f_0(p)=0$$\end{document}, all of whose maximum points are non-degenerate, we assume that the Paneitz operator is nonnegative and with kernel consisting of constants. Then, we are able to prove that for sufficiently small λ>0\documentclass[12pt]{minimal}
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\begin{document}$$\lambda >0$$\end{document} there are at least two distinct conformal metrics gλ=e2uλg0\documentclass[12pt]{minimal}
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\begin{document}$$g_\lambda =e^{2u_\lambda }g_0$$\end{document} and gλ=e2uλg0\documentclass[12pt]{minimal}
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\begin{document}$$g^\lambda =e^{2u^\lambda }g_0$$\end{document} of Q-curvature Qgλ=Qgλ=f0+λ\documentclass[12pt]{minimal}
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\begin{document}$$Q_{g_\lambda }=Q_{g^\lambda }=f_0+\lambda $$\end{document}. Moreover, by means of the “monotonicity trick” in a way similar to [9], we obtain crucial estimates for the “large” solutions uλ\documentclass[12pt]{minimal}
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\begin{document}$$u^\lambda $$\end{document} which enable us to study their “bubbling behavior” as λ↓0\documentclass[12pt]{minimal}
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\begin{document}$$\lambda \downarrow 0$$\end{document}.
