Solve the following problem:
Realize by PLA a BCD to Gray code converter, where the BCD number is represented by x1, x2, x3, x4 and the four outputs for the Gray code word y1, y2, y3, y4 are defined as
y1 = x1 + x2x4 + x2x3
y2 = x2x¯3
y3 = x2 + x3
y4 = x¯1x¯2x¯3x4 + x2x3x4 + x1x¯4 + x¯2x3x¯4.