What is the transitive closure of the relation R = -LCB- -LRB- b , a -RRB- , -LRB- b , e -RRB- , -LRB- c , b -RRB- , -LRB- c , d -RRB- , -LRB- e , d -RRB- -RCB- ?
How can I prevent a memory foam mattress from sinking ?