问题1：如何用图模型表达以下问题及其解？ There is a related mathematical question here.Let U and W be two sets.Does there exist a one-to-one function f:U>W? lU<=|W What if the image of each element of U cannot be just any element of W(an element of one prescibed subset of W)? 二部图：独立边！问题1:如何用图模型表达以下问题及其解？ • There is a related mathematical question here. Let U and W be two sets. Does there exist a one-to-one function f : U → W ? • What if the image of each element of U cannot be just any element of W (an element of one prescibed subset of W)? |U|<=|W| 二部图：独立边！