database - relational algebra of the query -

consider following relational database schemes:

courses (cno,name) pre-req(cno, pre-cno) completed (student_no, cno) 

courses gives number , name of available courses.

pre-req gives information courses pre-requisites given course.

completed indicates courses have been completed students

express following using relational algebra:

list courses student student_no = 2310 has completed pre-requisites.

the question can solved sql query unable derive equivalent relational algebra.

here's answer in tutorial d variant of ra:

with { compl_2310 := (completed student_no = '2310')                       { cno } rename { cno pre-cno }      } courses ( ( relation{ tuple{*} } join pre_req ){ pre-cno }               ⊆                 compl_2310               ) 

(this uses of introduced syntactic sugar , alternative syntax compared date & darwen's textbooks.)