% You can't have an argumentation engine without a tweety example.
% This example demonstrates an undercut of the rule, "most birds fly", based on the knowledge that penguins dont fly
% try querying "flies(tweety)".

penguin(tweety). $tweety is a penguin$
bird(X) <- penguin(X). $all penguins are birds$ ${X} is a bird$
[most_birds_fly(X)] flies(X) <- bird(X) 0.85. $most birds fly$ ${X} flies (probably)$
~most_birds_fly(X) <- penguin(X). $penguins don't fly$ $the "most birds fly" rule doesnt apply to {X}.$