An elementary minimax inequality (Q579612)

Let f and g be real valued functions defined on the Cartesian product \(X\times Y\) of nonempty sets X and Y. The paper gives a sufficient condition for validity of the inequality: \[ \inf_{y\in Y}\sup_{x\in X}f(x,y)\leq \sup_{x\in X}\inf_{y\in Y}g(x,y). \]