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Galois

Galois: A Language for Proofs Using Galois connections and ... - ALFA

Galois: A Language for Proofs Using Galois connections and ... - ALFA

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<strong>Galois</strong> connections<br />

Theoretical background<br />

<strong>Galois</strong> connections<br />

Definition (<strong>Galois</strong> connection)<br />

Given two preordered sets (A, ⊑ A ) and (B, ⊑ B ) and two functions<br />

B f<br />

A and g<br />

A B , the pair (f , g) is a <strong>Galois</strong> connection<br />

if and only if, for all a ∈ A and b ∈ B:<br />

f a ⊑ B b ⇔ a ⊑ A g b<br />

Graphical notation<br />

⊑ A<br />

A<br />

f<br />

g<br />

B<br />

⊑ B<br />

(f ,g)<br />

or (A, ⊑ A ) (B, ⊑ B )<br />

Paulo Silva (UMinho) <strong>Galois</strong> PLMMS’09 12 / 28

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