  Causal reasoning in relational domains is fundamental to studying real-world
social phenomena in which individual units can influence each other's traits
and behavior. Dynamics between interconnected units can be represented as an
instantiation of a relational causal model; however, causal reasoning over such
instantiation requires additional templating assumptions that capture feedback
loops of influence. Previous research has developed lifted representations to
address the relational nature of such dynamics but has strictly required that
the representation has no cycles. To facilitate cycles in relational
representation and learning, we introduce relational $\sigma$-separation, a new
criterion for understanding relational systems with feedback loops. We also
introduce a new lifted representation, $\sigma$-abstract ground graph which
helps with abstracting statistical independence relations in all possible
instantiations of the cyclic relational model. We show the necessary and
sufficient conditions for the completeness of $\sigma$-AGG and that relational
$\sigma$-separation is sound and complete in the presence of one or more cycles
with arbitrary length. To the best of our knowledge, this is the first work on
representation of and reasoning with cyclic relational causal models.
