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a^2 + 2ab + b^2
x^2 - 2xy + y^2
m^2 + 2mn + n^2
p^2 - 2pq + q^2
r^2 + 2rs + s^2
k^2 - 2kl + l^2
c^2 + 2cd + d^2
f^2 - 2fg + g^2
h^2 + 2hi + i^2
n^2 - 2no + o^2