In the expression (4.26) of f(x)

each variable appears both negated and not negated:

f(x) = x2x3x4 ∨ x4(x1 ∨ x2) ∨ x1x3(x2 ⊕ x4). (4.26)

Check by means of (4.24) and (4.25) whether function (4.26) is monotonously increasing or monotonously decreasing, separately with regard to each variable of the set {x1, x2, x3, x4}. Practical tasks:

1 Write a PRP that detects all monotone properties of the function (4.26)

with regard to each of its variables.

2 Execute this PRP and check for monotone properties.

3 Express the function in such a way that only one type of monotone variables occurs.

4 Verify the simplified expression of the function.