MathCheck Array Claim Problem 7 / 15

The array `xi` is indexed from `3` and contains `M` elements. Write a predicate saying that every element of `xi` occurs at least twice in `xi`. array_claim xi[3...M+2] f_nodes 30 AA z; 3 <= z < M+3: EE u; 3 <= u < M+3: u != z /\ xi[z] = xi[u] <=>

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