These papers by Luca Cardelli are quite good: http://lucacardelli.name/Papers/TypeSystems.pdf http://lucacardelli.name/Papers/TypeSystems.pdf http://lucacardell

These papers by Luca Cardelli are quite good: http://lucacardelli.name/Papers/TypeSystems.pdf http://lucacardelli.name/Papers/TypeSystems.pdf http://lucacardelli.name/Papers/OnUnderstanding.A4.pdf http://lucacardelli.name/Papers/OnUnderstanding.A4.pdf