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We present an observation for ZZ → ℓ+ ℓ-ℓ‘+ℓ‘- (ℓ, ℓ‘ = e or μ ) production in pp collisions at a center-of-mass energy of √s = 1.96 TeV. Using 1.7 fb-1 of data collected by the D0 experiment at the Fermilab Tevatron Collider, we observe three candidate events with an expected background of 0.14+0.03 -0.02 events. The significance of this observation is 5.3 standard deviations. The combination of D0 results in this channel, as well as in ZZ → ℓ+ ℓ-vv, yields a significance of 5.7 standard deviations and a combined cross section of σ (ZZ) = 1.60 ± 0.63(stat)+0.16 -0.17 (syst) pb.