Data update

Task/Symmetric-difference/Refal/symmetric-difference.refal

@@ -0,0 +1,28 @@
+$ENTRY Go {
+    , John Bob Mary Serena: e.A
+    , Jim Mary John Bob: e.B
+    = <Prout <Symdiff (e.A) (e.B)>>;
+};
+
+Symdiff {
+    (e.1) (e.2), <Diff (<Set e.1>) (<Set e.2>)>: e.3
+               , <Diff (<Set e.2>) (<Set e.1>)>: e.4
+               = <Union (e.3) (e.4)>;
+};
+
+Set {
+    = ;
+    s.1 e.1 s.1 e.2 = <Set e.1 s.1 e.2>;
+    s.1 e.1 = s.1 <Set e.1>;
+};
+
+Union {
+    (e.1) (e.2) = <Set e.1 e.2>;
+};
+
+Diff {
+    () (e.1) = ;
+    (e.1) () = e.1;
+    (s.1 e.1) (e.2 s.1 e.3) = <Diff (e.1) (e.2 e.3)>;
+    (s.1 e.1) (e.2) = s.1 <Diff (e.1) (e.2)>;
+};