Question: Let S be the set of all strings of English letters. Determine whether these relations are reflexive, irreflexive, symmetric, antisymmetric, and/or transitive.
a) R1 = {(a, b) | a and b have no letters in common}
b) R2 = {(a, b) | a and b are not the same length}
c) R3 = {(a, b) | a is longer than b}