How much higher in percentage does the word "grec" occur on the page titled "Àbac" than on the page titled "Astronomia"?
grec refers to word = 'grec'; Àbac refers to title = 'Àbac'; Astronomia refers to title = 'Astronomia'; percentage = DIVIDE(SUBTRACT(occurrences where title = 'Àbac' AND word = 'grec', occurrences where title = 'Astronomia' AND word = 'grec'), occurrences where title = 'Astronomia' AND word = 'grec')
SELECT CAST((SUM(CASE WHEN T3.title = 'Àbac' THEN T2.occurrences END) - SUM(CASE WHEN T3.title = 'Astronomia' THEN T2.occurrences END)) AS REAL) * 100 / SUM(CASE WHEN T3.title = 'Astronomia' THEN T2.occurrences END) FROM words AS T1 INNER JOIN pages_words AS T2 ON T1.wid = T2.wid INNER JOIN pages AS T3 ON T2.pid = T3.pid WHERE T1.word = 'grec'