Which papers' first author is affiliated with an institution in the country "Japan" and has last name "Ohori"? Give me the titles of the papers.
select t3.title from authors as t1 join authorship as t2 on t1.authid = t2.authid join papers as t3 on t2.paperid = t3.paperid join inst as t4 on t2.instid = t4.instid where t4.country = "Japan" and t2.authorder = 1 and t1.lname = "Ohori"