In Landau and Lifschitz Mechanics, p. 99, we have (implicit) the equality $$\Omega_i^2 x_i^2 = \Omega_i \Omega_k \delta_{ik} x_{\ell}^2 $$ written with Einstein summation convention.
The left hand side is clearly: $$\Omega_1^2x_1^2 + \Omega_2^2x_2^2+ \Omega_3^2x_3^2 $$
The answer to this question would indicate that the right hand side should be interpreted this way:
$$\Omega_i\Omega_k\delta_{ik}x_{\ell}^2 = \sum_i\sum_k \left[\Omega_i \Omega_k \delta_{ik} \left[\sum_{\ell} x_{\ell}^2 \right] \right] \\= \Omega_1^2[x_1^2+x_2^2+x_3^2] + \Omega_2^2[x_1^2 + x_2^2+x_3^2] + \Omega_3^2[x_1^2+x_2^2+x_3^2]$$
However, I only get that this is an identity when I interpret it this way:
$$\Omega_i\Omega_k\delta_{ik}x_{\ell}^2 = \sum_i\sum_k\sum_{\ell} \Omega_i\Omega_k\delta_{ik}x_{\ell}^2 = \Omega_1^2x_1^2 + \Omega_2^2x_2^2+ \Omega_3^2x_3^2 $$
So is there a mistake in the textbook? Or is the answer given to the other question incorrect? I've tried googling this, but all of the examples given are single terms, not multiple terms.
EDIT: The full equation in the textbook is (if it helps): $$\Omega_i^2 x_i^2 - \Omega_i x_i \Omega_k x_k = \Omega_i \Omega_k \delta_{ik} x_{\ell}^2 - \Omega_i \Omega_k x_i x_k $$