Phrase structure rules can be extended with LFG functional notations. The functional notation(s) of a symbol must be entered inside curly brackets.

*S → NP { (↑ SUBJ) = ↓; } VP { ↑ = ↓; };*

The parser can handle the following notation types

- defining equation
- constraining equation
- negative equation
- existential constraint
- negative existential constraint

**Defining equations**

A defining equation is an equation that contains the **equal sign** (=) or the **element of** (∈)

**equality equation**

In a functional notation, the **equal sign** (=) will unify the left and the right member. The value of both members will be replaced with the result of the unification.

S → NP

{

↑ = ↓;

}

Unification of the functional structure of the constituent NP (down arrow) with the functional structure of the constituent S (up arrow)

**membership equation**

The **element of** (∈) can be used to add the functional structure of the left constituent in a set (the right member)

NP → DET {↑=↓;} (ADJ)* { **↓ ∈ (↑MOD);**} N {↑=↓;};

Add the functional structure of every adjective to a set. The set is the value of the attribute MOD of the constituent NP (and also of the constituents DET, N because of the equality equation)