Element of Leibniz Harmonic Triangle as Sum of Elements on Diagonal from Below/Lemma 1

Theorem
Consider the Leibniz harmonic triangle:

Let $\tuple {n, m}$ be the element in the $n$th row and $m$th column.

Then:
 * $\tuple {n, m} = \tuple {n + 1, m} + \tuple {n + 1, m + 1}$

That is, each number in the Leibniz harmonic triangle is equal to the sum of the number below it and the number to the right of that number. This is similar to Pascal's Rule for Pascal's triangle.