--- /dev/null
+method f1(a b)
+ return not(a or b);
+end;
+
+method f2(a b)
+ return not(not(a or b));
+end;
+
+method f3(a b)
+ return not(a - b);
+end;
+
+method f4(a b)
+ return not(not(a - b));
+end;
+
+method f5(a b)
+ return not(a < b);
+end;
+
+method f6(a b)
+ return not(not(a < b));
+end;
+
+method f7(a b)
+ return not(a = b);
+end;
+
+method f8(a b)
+ return not(not(a = b));
+end;