CDA Fundamentals of Comp.S - Reduce an equation

how can I reduce:

$co = ci'ab+cia'b+ciab'+ciab$

to: $co = ab + cia + cib$

I don't know how they did that on the book... This is for Adders, working with circuits.

Thank you very much

• Whats means CDA? Is it Compact Disc Audio? And which book are you referring to? – J.-E. Pin Oct 11 '17 at 10:31
• ...........loool – Spyky Nov 1 '17 at 16:34

I am not an expert in circuits, but I have some doubt on your question. If you take $c = i = 0$ and $a = b = 1$, then $ci'ab+cia'b+ciab'+ciab = 0$ but $ab + cia + cib = 1$.