  We prove an analogue of Belyi's theorem in characteristic two. Our proof
consists of the following three steps. We first introduce a new notion called
"pseudo-tame" for morphisms between curves over an algebraically closed field
of characteristic two. Secondly, we prove the existence of a "pseudo-tame"
rational function by proving vanishing of an obstruction class. Finally we will
construct a tamely ramified rational function from the "pseudo-tame" rational
function.
