IF x1 = low, x2 = low THEN y = low
IF x1 = low, x2 = middle | high, x3 = low | middle THEN y = low
IF x1 = middle, x2 = low, x3 = low THEN y = low
IF x1 = middle, x2 = high, x3 = low THEN y = low

IF x1 = low, x2 = middle | high, x3 = high THEN y = middle
IF x1 = middle, x2 = middle, x3 = low | middle THEN y = middle
IF x1 = high, x3 = high THEN y = middle
IF x1 = high, x2 = low | middle, x3 = low THEN y = middle
IF x1 = high, x2 = high, x3 = low | middle THEN y = middle

IF x1 = middle, x2 = low, x3 = middle | high THEN y = high
IF x1 = middle | high, x2 = middle, x3 = high THEN y = high
IF x1 = middle | high, x2 = high, x3 = high THEN y = high
IF x1 = middle | high, x2 = middle, x3 = middle | high THEN y = high