I'm currently reading through the introduction section of a research paper which states the following:
Let $Y_0$, $Y_1$, $Y_2$ and $Y_3$ be independent uniformly distributed variables over the field $\mathbb{F_2=\{0,1\}}$. Then,
$P\left[ f(Y_0, Y_1, Y_2, Y_3)=0 \right] = 1/2$
where
$f(Y_0, Y_1, Y_2, Y_3) := \{\left( Y_0 \lor Y_1 \right)\oplus \left( Y_0 \land Y_3 \right) \}\oplus\{Y_2\land\left[\left(Y_0 \oplus Y_1\right) \lor Y_3\right]\}$
The paper offers only a proof "by inspection". After thinking about it for myself, it doesn't appear obvious to me to why this is true. Here is my thought process:
$P\left[Y_0\lor Y_1 = 0\right]=1/4$
$P\left[Y_0\land Y_3 = 0\right] = 3/4$
$P\left[\{\left( Y_0 \lor Y_1 \right)\oplus \left( Y_0 \land Y_3 \right) \}=0\right]=\frac{1}{4}\cdot\frac{3}{4}+\frac{3}{4}\cdot\frac{1}{4}=\frac{3}{8}$
$P\left[\left(Y_0 \oplus Y_1\right)=0\right]=1/2$
$P\left[\left[\left(Y_0 \oplus Y_1\right) \lor Y_3\right]=0\right]=1/4$
$P\left[\{Y_2\land\left[\left(Y_0 \oplus Y_1\right) \lor Y_3\right]\}=0\right]=1-\frac{1}{2}\cdot\frac{3}{4}=5/8$
$P\left[ f(Y_0, Y_1, Y_2, Y_3)=0 \right]=\frac{3}{8}\cdot\frac{5}{8}+\frac{5}{8}\cdot\frac{3}{8}=30/64=15/32\neq1/2$
Where is the fault in my understanding? What am I missing?