The document shows that the composition of two bijective functions is also a bijection. It defines three sets X, Y, W and bijective functions f: X->Y and g: Y->W. It then defines a function h: X->W as h(x) = g(f(x)). It proves h is bijective by showing it is both one-to-one and onto. It demonstrates one-to-one by showing each x maps to a unique w, and onto by showing each w maps back to some x. Therefore, the composition of f and g, defined as h, is a bijection from X to W.