Basic Ko Rule
The basic ko rule prohibits immediate recapture of a single stone that has just captured a single stone, as in the diagram below
This rule does not prevent longer cycles. Different rulesets have different rules for dealing with longer cycles, but all rulesets prevent basic kos.
 Robert Pauli: Well, "Natural" Situational Superko not always.
RobertJasiek: Basic ko is a terrible (page) alias for basic ko rule because a basic ko is a ko (shape) to which a basic ko rule might apply. The alias hides the term "basic ko", which is NOT the basic ko rule.
RobertJasiek: Herman, you have created a BasicKoRule alias but the BasicKo alias persists. What is your intention?