Half Adder using only the NOR gate

[Shajahan ES]

After trying and succeeding in making the HALF ADDER using the NAND
gate, I gave a try to make it solely using NOR gates, but failed so
many times... finally succeeded..
Here also, I’m posting only the part of finding the SUM, of course
you’ll have to find the CARRY using a AND gate (using a NOR gate
itself)
http://goforaplusplus.wordpress.com/2011/08/12/half-adder-using-only-the-nor-gate/