Article 19 of the Constitution provides: "The people shall have the duty to pay tax under law." Article 1 of the Estate and Gift Taxes Act provides: "Where a national of the Republic of China who regularly resided in the territory of the Republic of China left property at the time of his death, an estate tax shall be levied under this Act upon all estates owned by him in and outside the Republic of China; where a national of the Republic of China who regularly resided outside the territory of the Republic of China or a person who was not a national of the Republic of China left property in the territory of the Republic of China at the time of his death, an estate tax shall be levied under this Act upon all estates owned by him in the Republic of China." And, under the same Act, the heir has the duty to declare and pay tax pursuant to the levying procedure set forth therein. Furthermore, the Act provides in Article 17, Paragraph 1, Subparagraph 8, that debts of the decedent not repaid prior to his death and verifiable by substantial proof are deductible from the gross amount of the estate. However, granted that debts were contracted or property was sold by the decedent during the time when he was incapable of managing his business because of serious illness, it would, generally speaking, be difficult for him to personally manage the use of the money so borrowed or the proceeds of the sale of his property. Thus, the heir must of course be required to prove the usage of such money or proceeds to prevent the heir from mismanaging the estate through the accumulation of debts or sale of property in the name of the decedent. To give full effect to Article 1 and Article 17, Paragraph 1, Subparagraph 8, of the Estate and Gift Taxes Act, the Enforcement Rules provide in Article 13: " Where a decedent contracted any debt or sold any of his property before his death and during the period in which he was incapable of managing his business because of serious illness, and his heir is unable to prove the usage of the money so borrowed or the proceeds obtained, such money shall be included in the estate for tax purposes." The purpose of this article is to insure correct accounting of the taxable estate as well as to protect the interest of the heir, and is essential to the prevention of possible evasion of estate tax and the maintenance of equality in taxation. It does not add any taxation to what is legally imposed on the people and is hence not inconsistent with Article 19 of the Constitution. As to whether there is any taxable estate in a particular case, either the taxing authority or the taxpayer must be required to assume the burden of proof, as the case may be, under the doctrine of distribution of the burden of proof.