The mere failure to comply with certain formalities prescribed by a state law is not, without reference to what those formalities are, a denial of due process. "When, then, a state court decides that a particular formality was or was not essential under a state statute, such decision presents no federal question, providing always that the statute as thus construed does not violate the Constitution of the United States by depriving of property without due process of law. This paramount requirement being fulfilled, as to other matters the state interpretation of its own law is controlling and decisive." 27