# Normal form

The term normal form is used in a variety of contexts. Many of the uses in mathematics are special cases of a single situation, looked at abstractly: within an equivalence class one specifies a representative element, which is in a simplest or most manageable or otherwise tidiest and most desirable form, in terms of structure or syntax. A little more loosely, an equivalence class might contain several examples of such special, distinguished elements. For example, the Jordan normal form under similarity of matrices (link below) may mean any suitable block matrix in similarity class, and in the general case there can be several such.

In classical logic, propositions may be in:

In relational database theory

• first normal form
• second normal form
• third normal form
• fourth normal form
• fifth normal form

see database normalization for all four.

In the lambda calculus

• the normal form of a pitch or pitch class set, which is the order that occupies the smallest possible span and is stacked leftmost.

To transform something into a normal form is often called normalization.

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