Database: academic
Question: return me the number of keywords in the papers of " University of Michigan " .
SQL:
SELECT COUNT ( DISTINCT t1.keyword ) FROM organization AS t6 JOIN author AS t2 ON t6.oid  =  t2.oid JOIN writes AS t4 ON t4.aid  =  t2.aid JOIN publication AS t5 ON t4.pid  =  t5.pid JOIN publication_keyword AS t3 ON t5.pid  =  t3.pid JOIN keyword AS t1 ON t3.kid  =  t1.kid WHERE t6.name  =  "University of Michigan";