European green woodpecker though the latter is smaller and more slender with narrower wings and longer tail. The closely related, very similar Levaillant's woodpecker occurs only in north-west Africa. The European green woodpecker is a member of the order Piciformes, the woodpecker family Picidae and the genus Picus. It was first described by Linnaeus in 1758. The scientific name is derived from the Greek "pikos", meaning 'woodpecker', and Latin "viridis", 'green'. There are four subspecies, with subtle and mostly clinal differences between them. In a recent study based on mitochondrial DNA analysis of subspecies by Perktaş, Barrowclough and Groth, it has been proposed
An Essay on the Nature and Significance of Economic Science on economic methodology in generating a range of tightly-argued, radical implications from a simple definition, for example in admitting an "aspect" of behaviour (rather than a list of behaviours) but not limiting the subject-matter of economics, provided that the influence of scarcity impinges on these (pp. 16–17). The broad behavioural definition is credited for its consistency with the expanding boundaries of economics decades later. In this Robbins both narrows the definition of economics, thereby demonstrating the usefulness of deduction, and opens up the subject-matter of economics. Robbins's "Essay" is one of the most-cited works on the methodology and philosophy of