Coupling p,g:distributions over a distribution u over x is a coupling of p,q ifp(x)=>μ(，) q(c)=∑(y,x) y∈2 y∈2 9 0 2 p 2Coupling p(x) = X y2⌦ µ(x, y) q(x) = X y2⌦ µ(y, x) a distribution µ over ⌦ ⇥ ⌦ is a coupling of p,q p,q : distributions over ⌦ if µ ⌦ ⌦ p q