I am using an expression in a paper which doesnt need a proof at all such as $\sum_{i=k}^K\binom{K}{i}p^i(1-p)^{K-i}$ is a decreasing function of $k$ and $\sum_{i=0}^{k-1}\binom{K}{i}p^{K-i}(1-p)^i$ is an increasing function of $k$. However I connot write it in the text. Because I refer to this property in a non trivial proposition.
Question: How should I put this thing in a format? should I call it as a statement or definition or corollary?
Thank you very much.