Show that $(M(X,\mathcal{A},\mathbb{R}),\leq)$ defines a lattice.
I know that $M(X,\mathcal{A},\mathbb{R})$ with the relation $\leq$ defines a partial order. Now, a lattice consists of a partially ordered set in which every two elements have a unique supremun and infimum.
But I really have no idea on how to proceed. I have read about Hasse diagrams but I don't think I can apply that here.
I'd appreciate any help!