Hi, I've been trying to work out the formula for the sum for the full adder logic, however have come across a gap which I don't know how to fill. S = (¬A.¬B.C) + (¬A.B.¬C) + (A.¬B.¬C) + (A.B.C) S = ¬A.(¬B.C + B.¬C) + A.(¬B.¬C) S = ¬A.(B [tex]\oplus[/tex] C) + A.( do not know what to do at this point to reach the next stage S = (A [tex]\oplus[/tex] B) [tex]\oplus[/tex] C Does anyone know how to get to that last statement? Thanks for any help.