Consider the solutions of
capillary surface equation with contact angle boundary condition over domains with
corners. It is known that if the corner angle 2α satisfies 0 < 2α < π and α + γ > π∕2
where 0 < γ ≤ π∕2 is the contact angle, then solutions are regular. It is also
known that no regularity holds in case α + γ < π∕2. In this paper we show
that solutions are still regular for the borderline case α + γ = π∕2 at the
corner.