**Types and Relations**

Several of the entries appearing in this part of the dictionary—primarily ones having to do with type theory—are expanded or elaborated on in Part II (“Inheritance”). Such entries are marked “Without inheritance” in what follows (and the corresponding expanded entries in Part II are marked “With inheritance” accordingly).

**0-adic** (*Of an operator or predicate*) Niladic. *Contrast* 0-ary.

**0-ary** (*Of a heading, key, tuple, relation, etc*.) Of degree zero. *Contrast* 0-adic.

**0-place** (*Of a predicate*) Niladic.

**0-tuple** The empty tuple; the tuple of degree zero.

**1NF** First normal form.

**2NF** Second normal form.

**2VL** Two-valued logic.

**3NF** Third normal form.

**3VL** Three-valued logic.

**4NF** Fourth normal form.

**4VL** Four-valued logic.

**5NF** Fifth normal form.

**6NF** Sixth normal form.

**A** A relationally complete (q.v.), “reduced instruction set” version of relational algebra with just two primitive operators—REMOVE (essentially projection on all attributes but one), q.v., and an algebraic analog of either NOR or NAND, q.v. The name **A** (note the boldface) is a doubly recursive acronym: It stands for *ALGEBRA*, which in turn stands for *A Logical Genesis Explains Basic Relational Algebra*. As this expanded name suggests, the algebra **A** is designed in such a way as to emphasize its close relationship ...

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