Find the minimum SOP and POS expression for the following functions using Karnaugh Map and realize the expression using appropriate gates. Also realize SOP form using NAND-to-NAND gate network and convert this gate network to a AND-to-OR gate network. Use as few gates as possible.
 
1. F(W,X,Y,Z) = ∑m (0,1,3,4,6,12,13,14,15) + ∑d (2,5,7)

2. F(A,B,C,D) =  ∑m (0,1,2,7,8,10) + ∑d (5,6,11,15)

3. F(A,B,C,D) =  ∑m (0,1,2,3,7,8,10) + ∑d (5,6,11,15)

Here, m represents minterms and d represents Don't care conditions