In the following formula :
I substituted :
1)|x+y|=|x|+|y| with a
2) with b
3)x+y=|x|+|y| with c
4) x+y<0 with d
5) x+y = -|x|-|y| with e
Then
I tried to write the truth table of :
expecting to get a tautology.
But unfortunately i did not get a tautology. Why?
Does that mean that the above formula in not provable??