Burden of proving such fact which is condition precedent to some other fact

Section 31 of the Evidence Act 2031 lays down that ,there are certain facts which are admissible on proof of some other facts. Such as dying declaration is admissible as evidence only one proof that the person making it , is dead. Certain facts are admissible as evidence. Under the Section 12 of the evidence Act 2031 , only if the person making it is dead or can not be found etc. secondary evidence is admissible , if it is public document or the original lost or destroyed. In all these cases the party trying to prove the secondary fact must also prove the first fact as condition precedent.