adding graph:term built-in

VERSION

@@ -1 +1 @@
-1.4.1
+1.4.2

cases/output/socrates.trig

@@ -1,3 +1,21 @@
-PREFIX : <https://eyereasoner.github.io/lingua/cases/socrates.trig#>
+PREFIX graph: <http://www.w3.org/2000/10/swap/graph#>
+PREFIX var: <http://www.w3.org/2000/10/swap/var#>
+PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
 
-:Socrates a :Mortal.
+_:node_1_1 graph:term _:node_1_1.
+_:node_1_1 graph:member _:bng_1.
+_:node_4_1 graph:term _:node_4_1.
+_:node_4_1 graph:member _:node_4_1.
+
+GRAPH _:node_1_1 {
+    var:A rdfs:subClassOf var:B.
+    var:S a var:A.
+}
+
+GRAPH _:bng_1 {
+    var:A rdfs:subClassOf var:B.
+}
+
+GRAPH _:node_4_1 {
+    var:X rdfs:subClassOf var:Y.
+}

cases/socrates.trig

@@ -5,6 +5,7 @@
 # Infer that Socrates is mortal.
 
 PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
+PREFIX graph: <http://www.w3.org/2000/10/swap/graph#>
 PREFIX log: <http://www.w3.org/2000/10/swap/log#>
 PREFIX var: <http://www.w3.org/2000/10/swap/var#>
 PREFIX : <#>
@@ -29,5 +30,10 @@ GRAPH _:bng_2 {
 _:bng_3 log:query _:bng_3.
 
 GRAPH _:bng_3 {
-    var:S a :Mortal.
+    var:S graph:term var:O.
+    var:O graph:member _:bng_4.
+}
+
+GRAPH _:bng_4 {
+    var:X rdfs:subClassOf var:Y.
 }

lingua.pl

@@ -19,7 +19,7 @@
 :- use_module(library(semweb/turtle)).
 :- catch(use_module(library(http/http_open)), _, true).
 
-version_info('lingua v1.4.1').
+version_info('lingua v1.4.2').
 
 help_info('Usage: lingua <options>* <data>*
 
@@ -265,9 +265,6 @@
     % remove rdf reifiers
     retractall('<http://www.w3.org/1999/02/22-rdf-syntax-ns#reifies>'(_, _)),
 
-    % remove rdf named graphs
-    retractall(graph(_, _)),
-
     % create forward rules
     assertz(implies((
             '<http://www.w3.org/2000/10/swap/log#implies>'(A, B),
@@ -1417,6 +1414,9 @@
         )
     ).
 
+'<http://www.w3.org/2000/10/swap/graph#term>'(A, B) :-
+    graph(A, B).
+
 '<http://www.w3.org/2000/10/swap/graph#union>'(A, B) :-
     when(
         (   nonvar(A)