| To express the general case of <math>\nu_k~\!</math> in terms of familiar operations, it helps to introduce an intermediary concept: | | To express the general case of <math>\nu_k~\!</math> in terms of familiar operations, it helps to introduce an intermediary concept: |
− | '''Definition.''' Let the function <math>\lnot_j : \mathbb{B}^k \to \mathbb{B}~\!</math> be defined for each integer <math>j~\!</math> in the interval <math>[1, k]~\!</math> by the following equation: | + | '''Definition.''' Let the function <math>\lnot_j : \mathbb{B}^k \to \mathbb{B}~\!</math> be defined for each integer <math>j~\!</math> in the interval <math>[1, k]~\!</math> by the following equation: |
− | If we think of the point <math>x = (x_1, \ldots, x_k) \in \mathbb{B}^k~\!</math> as indicated by the boolean product <math>x_1 \cdot \ldots \cdot x_k~\!</math> or the logical conjunction <math>x_1 \land \ldots \land x_k,~\!</math> then the minimal negation <math>\texttt{(} x_1, \ldots, x_k \texttt{)}~\!</math> indicates the set of points in <math>\mathbb{B}^k~\!</math> that differ from <math>x~\!</math> in exactly one coordinate. This makes <math>\texttt{(} x_1, \ldots, x_k \texttt{)}~\!</math> a discrete functional analogue of a ''point omitted neighborhood'' in analysis, more exactly, a ''point omitted distance one neighborhood''. In this light, the minimal negation operator can be recognized as a differential construction, an observation that opens a very wide field. It also serves to explain a variety of other names for the same concept, for example, ''logical boundary operator'', ''limen operator'', ''least action operator'', or ''hedge operator'', to name but a few. The rationale for these names is visible in the venn diagrams of the corresponding operations on sets. | + | If we take the boolean product <math>x_1 \cdot \ldots \cdot x_k~\!</math> or the logical conjunction <math>x_1 \land \ldots \land x_k~\!</math> to indicate the point <math>x = (x_1, \ldots, x_k)~\!</math> in the space <math>\mathbb{B}^k~\!</math> then the minimal negation <math>\texttt{(} x_1 \texttt{,} \ldots \texttt{,} x_k \texttt{)}~\!</math> indicates the set of points in <math>\mathbb{B}^k~\!</math> that differ from <math>x~\!</math> in exactly one coordinate. This makes <math>\texttt{(} x_1 \texttt{,} \ldots \texttt{,} x_k \texttt{)}~\!</math> a discrete functional analogue of a point-omitted neighborhood in ordinary real analysis, more exactly, a point-omitted distance-one neighborhood. In this light, the minimal negation operator can be recognized as a differential construction, an observation that opens a very wide field. |
− | The remainder of this discussion proceeds on the ''algebraic boolean convention'' that the plus sign <math>(+)~\!</math> and the summation symbol <math>(\textstyle\sum)~\!</math> both refer to addition modulo 2. Unless otherwise noted, the boolean domain <math>\mathbb{B} = \{ 0, 1 \}~\!</math> is interpreted so that <math>0 = \mathrm{false}~\!</math> and <math>1 = \mathrm{true}.~\!</math> This has the following consequences: | + | The remainder of this discussion proceeds on the algebraic convention that the plus sign <math>(+)~\!</math> and the summation symbol <math>(\textstyle\sum)~\!</math> both refer to addition mod 2. Unless otherwise noted, the boolean domain <math>\mathbb{B} = \{ 0, 1 \}~\!</math> is interpreted for logic in such a way that <math>0 = \mathrm{false}~\!</math> and <math>1 = \mathrm{true}.~\!</math> This has the following consequences: |
− | | The inclusive disjunctions indicated for the <math>\nu_k~\!</math> of more than one argument may be replaced with exclusive disjunctions without affecting the meaning, since the terms disjoined are already disjoint. | + | | The inclusive disjunctions indicated for the <math>\nu_k~\!</math> of more than one argument may be replaced with exclusive disjunctions without affecting the meaning since the terms in disjunction are already disjoint. |