Using only logical connectives (A, V, etc.), =, #, s+, X, 0, 1, 2, variables, and quantifiers write the following predicates concerning natural numbers. Try to make your answer as succinct as possible. (a) "r is a sum of two squares of natural numbers." (b) "ris a common divisor of y and 2." (c) "r is the greatest common divisor of y and 2." (d) "is a composite number." (A composite number is a number formed by mul- tiplying two smaller natural numbers.)