Equations for l2norm-kernel-v1
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  l2norm
    formula:  ||x|| = sqrt(Σ x_i²)
    domain:   x ∈ ℝ^n
    codomain: [0, ∞)
    invariants:
      - ||x|| ≥ 0
      - ||α·x|| = |α|·||x||
      - ||0|| = 0

