Consider in a real Hilbert space H the differential equation (inclusion) (E): p(t)u''(t)+q(t)u'(t) \in Au(t) + f(t) a.e. in (0, \infty) , with the condition (B): u(0) = x \in \overline{D(A)} , where A :D(A)\subset H\rightarrow H is a (possibly set-valued) maximal monotone operator whose range contains 0 ; p, q\in L^{\infty}(0,\infty ) , such that \mathrm{ess} \inf \ p>0 , \frac{q}{p} is differentiable a.e., and \mathrm{ess} \inf \, \big[{(\frac{q}{p})}^2 + 2(\frac{q}{p})^{\prime}\big] >0 . We prove existence of a unique (weak or strong) solution u to (E), (B), satisfying a^{\frac{1}{2}}u \in L^{\infty}(0,\infty ;H) and t^{\frac{1}{2}}a^{\frac{1}{2}}u^{\prime} \in L^2(0,\infty ;H) , where a(t)=\exp{\big( \int_0^t \frac{q}{p}\, d\tau \big) } , showing in particular the behavior of u as t\rightarrow \infty .
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