**commit** 1f1e65822f6ec9f08f8eb278f6b44dbebd6ed244
**parent** 4d68bb16130ee0a76df52aa96786b5ec1b8fd9c0
**Author:** a3nm <>
**Date:** Sun, 17 Jun 2018 02:11:39 +0200
functions
**Diffstat:**

1 file changed, 2 insertions(+), 0 deletions(-)

**diff --git a/Logic.page b/Logic.page**
@@ -2,6 +2,8 @@
A **signature** (with relation names and arities) is defined [like in databases](Basic database terminology#signatures). A **structure** for a signature $\sigma$ consists of a **domain** of elements and an **interpretation** for each relation $R$ of $\sigma$, i.e., a set of $n$-tuples of elements of the domain, where $n$ is the arity of $R$. This definition is similar to that of a [database instance](Basic database terminology#instances) except that the domain is explicitly given, and it may be the case that some domain elements do not occur in the interpretation of any relation.
+Unlike in some mathematical fields, none of the logics presented here feature **function symbols**, so we are defining **function-free logics** in the terminology of these fields.
+
# First-order logic
A **first-order logic** formula is defined over a [signature](Basic database terminology#signatures) $\sigma$, and consists of an expression built from [atoms](Basic database terminology#facts-and-atoms) and using