• A
sorting algorithm is an abstract structure, but a
recipe is not, because it depends on the properties and quantities of its ingredients. • A simple
melody is an abstract structure, but an
orchestration is not, because it depends on the properties of particular instruments. •
Euclidean geometry is an abstract structure, but the theory of
continental drift is not, because it depends on the geology of the
Earth. • A
formal language is an abstract structure, but a
natural language is not, because its rules of grammar and syntax are open to debate and interpretation. == Notes ==