  The paper investigates navigability with imperfect information. It shows that
the properties of navigability with perfect recall are exactly those captured
by Armstrong's axioms from the database theory. If the assumption of perfect
recall is omitted, then Armstrong's transitivity axiom is not valid, but it can
be replaced by two new weaker principles. The main technical results are
soundness and completeness theorems for the logical systems describing
properties of navigability with and without perfect recall.
