Full Idea
Entailment is modelled in formal semantics as set inclusion. 'Cat' entails 'mammal' because the cats are a subset of the mammals.
Gist of Idea
Entailment is modelled in formal semantics as set inclusion (where 'mammals' contains 'cats')
Source
Dougherty,T/Rysiew,P (What is Knowledge-First Epistemology? [2014], p.10)
Book Reference
'Contemporary Debates in Epistemology (2nd ed)', ed/tr. Steup/Turri/Sosa [Wiley Blackwell 2014], p.10
A Reaction
I would have thought that this was only one type of entailment. 'Travelling to Iceland entails flying'. Travelling includes flying, the reverse of cats/mammals, to a very complex set-theoretic account is needed. Interesting.