Presumptions.
(d) any person who is found to have had in his custody or under his control anything whatsoever
containing any dangerous drug shall, until the contrary is proved, be deemed to have been in possession
of such drug and shall, until the contrary is proved, be deemed to have known the nature of such drug;
(da) any person who is found in possession of—
(i) 15 grammes or more in weight of heroin;
otherwise than in accordance with the authority of this Act or any other written law, shall be presumed,
until the contrary is proved, to be trafficking in the said drug;