CREATE TABLE field (fieldid INT)
CREATE TABLE author (authorid INT, authorname VARCHAR)
CREATE TABLE venue (venueid INT, venuename VARCHAR)
CREATE TABLE dataset (datasetid INT, datasetname VARCHAR)
CREATE TABLE paperkeyphrase (paperid INT, keyphraseid INT)
CREATE TABLE paperdataset (paperid INT, datasetid INT)
CREATE TABLE cite (citingpaperid INT, citedpaperid INT)
CREATE TABLE keyphrase (keyphraseid INT, keyphrasename VARCHAR)
CREATE TABLE paperfield (fieldid INT, paperid INT)
CREATE TABLE journal (journalid INT, journalname VARCHAR)
CREATE TABLE paper (paperid INT, title VARCHAR, venueid INT, year INT, numciting INT, numcitedby INT, journalid INT)
CREATE TABLE writes (paperid INT, authorid INT)

keyphrases used by Akihito Kotera and Masatsugu Kidode
SELECT DISTINCT paperkeyphrase.keyphraseid FROM author, paperkeyphrase, writes WHERE author.authorname IN ('Akihito Kotera', 'Masatsugu Kidode') AND writes.authorid = author.authorid AND writes.paperid = paperkeyphrase.paperid GROUP BY paperkeyphrase.keyphraseid HAVING COUNT(DISTINCT writes.authorid) = 2
SELECT DISTINCT "paperkeyphrase"."keyphraseid" FROM "author" JOIN "writes" ON "author"."authorid" = "writes"."authorid" JOIN "paperkeyphrase" ON "paperkeyphrase"."paperid" = "writes"."paperid" WHERE "author"."authorname" IN ('Akihito Kotera', 'Masatsugu Kidode') GROUP BY "paperkeyphrase"."keyphraseid" HAVING COUNT(DISTINCT "writes"."authorid") = 2