adding graph equality example

etc/equality.trig

@@ -0,0 +1,37 @@
+# ----------------------
+# Graph equality example
+# ----------------------
+
+PREFIX log: <http://www.w3.org/2000/10/swap/log#>
+PREFIX lingua: <http://www.w3.org/2000/10/swap/lingua#>
+PREFIX var: <http://www.w3.org/2000/10/swap/var#>
+PREFIX : <#>
+
+GRAPH _:bng_1 {
+    :A :B :C.
+    :D :E _:bng_2.
+}
+
+GRAPH _:bng_2 {
+    :F :G var:H.
+}
+
+GRAPH _:bng_3 {
+    :D :E _:bng_4.
+    :A :B :C.
+}
+
+GRAPH _:bng_4 {
+    :F :G var:I.
+}
+
+#query
+_:bng_5 lingua:answer _:bng_6.
+
+GRAPH _:bng_5 {
+    _:bng_1 log:equalTo _:bng_3.
+}
+
+GRAPH _:bng_6 {
+    :test :is true.
+}

etc/output/equality.trig

@@ -0,0 +1,33 @@
+PREFIX : <https://eyereasoner.github.io/lingua/etc/equality.trig#>
+PREFIX lingua: <http://www.w3.org/2000/10/swap/lingua#>
+PREFIX log: <http://www.w3.org/2000/10/swap/log#>
+
+:test :is true.
+
+#
+# lingua explanation
+#
+
+_:bng_1 lingua:explanation _:bng_2.
+
+GRAPH _:bng_5 {
+    :F :G _:sk_0.
+}
+
+GRAPH _:bng_1 {
+    _:bng_3 log:equalTo _:bng_4.
+}
+
+GRAPH _:bng_2 {
+    :test :is true.
+}
+
+GRAPH _:bng_3 {
+    :A :B :C.
+    :D :E _:bng_5.
+}
+
+GRAPH _:bng_4 {
+    :D :E _:bng_5.
+    :A :B :C.
+}