A3 A2 A1 A->Y
0 0 0 0 Y=1 
1 0 0 0 Y=0 
1 1 0 0 Y=0 
0 1 0 0 Y=0 
0 1 1 0 Y=0 
1 1 1 0 Y=0 
1 0 1 0 Y=0 
0 0 1 0 Y=0 
0 0 1 1 Y=0 
1 0 1 1 Y=0 
1 1 1 1 Y=0 
0 1 1 1 Y=0 
0 1 0 1 Y=0 
1 1 0 1 Y=0 
1 0 0 1 Y=0 
0 0 0 1 Y=0 
function: Y = (!A3 && !A2 && !A1 && !A)