Why is x'+y

x'	y	x'+y
0	0	1
1	0	1
0	1	0
1	1	1

and not

x'	y	x'+y
0	0	1
1	0	0
0	1	1
1	1	1

Please explain why it is the first table and not the second. I am trying to workout the problem but I am not understanding the logic.

Thanks!