BIO v. YEBOAH Evidence—Admissibility—Hearsay—Documentary evidence—Conditions for admission of such evidence—Admissibility of letter as to facts in issue—Writer not called to testify even though available—Admission of letter infringing hearsay rule at common law and under NRCD 323, s 117—Circumstances when such hearsay evidence admissible under Order 37, rr 60 and 61—Evidence Decree 1975, (NRCD 323), s. 117—High Court (Civil Procedure) Rules, 1954 (L.N 140A), Order 37, rr 60 and 61.