1) Draw a 4 bit adder subtractor circuit. In addition to 4 bit inputs a and b another input is sub. When sub is high the output is a-b else the output is a+b. In addition to the above 4 bits output cout, the carry out of the MSB bit is another output. Try to minimize logic used.

2)A symmetrical boolean is a boolean function whose value does not depend on the permutation of its input bits i.e only depends only on the number ones in the input . For example XOR is a symmetrical boolean function. As another example for a 3 input boolean function the output for inputs 001,010,100 must be the same. How many symmetrical boolean functions of n inputs are there?

3)A two's complement adder takes in 2 n-bit numbers and produces an n-bit output and cout,the carry out of the MSB (assume carry bits are also available for used). What logic is required to compute the overflow?