Find sailors rated > 7 who’ve reserved boat #103

{S | (S ? Sailors) ^ (S.rating > 7) ^ (? R ? Reserves (R.sid = S.sid ^ R.bid = 103))}

Note the use of ? to find a tuple in Reserves that `joins with’ the Sailors tuple under consideration.

{S | (S ? Sailors) ^ (S.rating > 7) ^ (? R ? Reserves (R.sid = S.sid ^ R.bid = 103))}