Its semantics are defined using finite structure (mathematical logic).

The set of σ-sentences valid in all finite structures is not recursively enumerable.

Another contribution of his was the introduction of finite and non-continuous structures into geometry.

In other words, we find the following finite clausal structures:

To study computation we need a theory of finite structures.

For a single finite structure this is always possible.

Is a Language L expressive enough to describe exactly those finite structures that have certain property P in common (up to isomorphy)?

The queries - when restricted to finite structures - correspond to the computational problems of traditional complexity theory.

Conversely, the table of any finite structure can be encoded by a finite string.

Some of the finite structures considered in graph theory have names, sometimes inspired by the graph's topology, and sometimes after their discoverer.