6. Let A be the set of letters in the English alphabet. For each of the following relations on A, decide if it is re- flexive, irreflexive, transitive, or antisymmetric. (Each can satisfy more than one of these properties.) (a) R1 ( ? ?, ?) EA x A : ? immediately precedes in alphabetical order) (b) R2-(?, ?) e A x A : ? comes before ? in alpha- betical order