If M + n = P + Q, M N P Q ∈ n *, there is am + an = AP + AQ in the arithmetic sequence, what about in the arithmetic sequence?

If M + n = P + Q, M N P Q ∈ n *, there is am + an = AP + AQ in the arithmetic sequence, what about in the arithmetic sequence?

By analogy, a [M] * a [n] = a [P] * a [q]