CREATE TABLE authorship (instid VARCHAR, paperid VARCHAR)
CREATE TABLE papers (paperid VARCHAR)
CREATE TABLE inst (country VARCHAR, instid VARCHAR)

Retrieve the country that has published the most papers.
SELECT t1.country FROM inst AS t1 JOIN authorship AS t2 ON t1.instid = t2.instid JOIN papers AS t3 ON t2.paperid = t3.paperid GROUP BY t1.country ORDER BY COUNT(*) DESC LIMIT 1
SELECT "t1"."country" FROM "inst" AS "t1" JOIN "authorship" AS "t2" ON "t1"."instid" = "t2"."instid" JOIN "papers" AS "t3" ON "t2"."paperid" = "t3"."paperid" GROUP BY "t1"."country" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1