# Stratified negation: derive isolated nodes that have no outgoing edges.
#
# This example uses negation-as-failure (NOT) in a rule body. The chase
# evaluates rules in stratified order so that Connected/1 is fully
# materialized before Isolated/1 checks for its absence.
#
# NOTE: this script requires chase_stratified(), which is available via
# the Rust API. The REPL currently runs the non-stratified chase, so
# negation here works correctly only when the negated predicate is never
# derived by another rule in the same stratum.

fact Node(a).
fact Node(b).
fact Node(c).
fact Node(d).
fact Edge(a, b).
fact Edge(b, c).

# Copy edges to a unary Connected predicate.
rule Edge(?X, ?Y) -> Connected(?X).

# Nodes without outgoing edges are isolated.
# (In the REPL's single-stratum chase this fires correctly because
# Connected is derived from Edge, which is a base predicate.)
rule Node(?X), NOT Connected(?X) -> Isolated(?X).

run.
query Isolated(?X)?