# Submodularity

For the sets ${\displaystyle A\subseteq B}$ and an additional element ${\displaystyle s}$ that is not ${\displaystyle B}$. A cost (or reward) function on these sets is said to be sumbodular if
${\displaystyle R(A\cup \{s\})-R(A)\geq R(B\cup \{s\})-R(B)}$