selecting FYP(final year project)

FYP is the only thing that posibbly determine your life for the next one year~ so one must really put choose well~~ Arrg~

suddenly remember this thing i saw on a whiteboard at a training shed in army~ this is something that i have seen before about 10 years back which used to amaze me~ 10 years have past and i see this again, i realise the flaw in this argument... the argument is as follows:

let x = y
1) add x to both sides
=> 2x = x + y
2) subtract 2 y to both sides~
=> 2x - 2 y = x-y
3) can everyone see whats coming? after factorizing x-y
=> 2(x-y) = (x-y)
=> 2 = 1 ~!?~!?~!?