Translation of Sigma Query

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The query in mathematical notation is: St(*) (Sx,y;v1(*) world-map)

where v1= x1 < x < x2 & y1 < y < y2 & course-title = "visual languages"

In SQL-like language the query is:

SELECT     t
CLUSTER    *
FROM       SELECT x,y
           CLUSTER *
           FROM world-map
           WHERE x1 < x  < x2 and
                 y1 < y < y2  and
                 course-title = "visual languages"