Extensions

• Computability Logic - Wikipedia (free encyclopedia) article.
• Infinitary Logic - Article in the Stanford Encyclopaedia of Philosophy by John L. Bell. Infinitary Logic is a branch of formal logic where finitary formulae are replaced by potentially infinitary mathematical entities.
• Logic System Interrelationships - Shows how a number of representative logics fit together. The interrelationships usually given as something of the form: System X is system Y plus the axiom Z. By John Halleck.
• Non Standard Logics - A comprehensive listing of flavours of non-standard logic with brief descriptions and references, compiled by Peter Suber.
• What are Weak Arithmetics - Notes defining the subject. Available in HTML and PS formats.