1 - d^2 + 2dp - p^2 = 1 - (d^2 - 2dp + p^2) = 1 - (d - p)^2 =
= 1^2 - (d - p)^2 = (1 - (d-p))(1 + (d-p)) = (1 - d + p)(1 + d - p)
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