Example 3.2. The N-structure, (X, η) on a BF-algebra X in the Examplle
2.3 defined by
η(x) =
−0.3 ; x = 0, 2
0 ; x = 1, 3, 4
is an N-Ideal of X.
Definition 3.3. An N-structure (X, η) on a BF-algebra X is said to be a
N-structured Closed Ideal (NC-Ideal) of X if
(i) η(x) ≤ η(x ∗ y) ∨ η(y) and (ii) η(0 ∗ x) ≤ η(x) ∀x, y ∈ X