Ejemplo n.º 1
0
        public void PriorityUnion()
        {
            Func <FeatureStruct, FeatureStruct, FeatureStruct> resultsSelector = (fs1, fs2) =>
            {
                fs1.PriorityUnion(fs2);
                return(fs1);
            };
            Func <FeatureStruct, FeatureStruct, VariableBindings, FeatureStruct> varResultsSelector = (fs1, fs2, varBindings) =>
            {
                fs1.PriorityUnion(fs2, varBindings);
                return(fs1);
            };

            TestBinaryOperation(FreezableEqualityComparer <FeatureStruct> .Default, resultsSelector, varResultsSelector,
                                // simple
                                featSys => FeatureStruct.New(featSys).Symbol("a2").Symbol("b1").Symbol("c2").Value,
                                featSys => FeatureStruct.New(featSys).Symbol("a2").Symbol("b1").Symbol("c2").Value,

                                // complex
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol("a2"))
                                .Feature("cx2").EqualTo(cx2 => cx2.Symbol("b1"))
                                .Feature("cx3").EqualTo(cx2 => cx2.Symbol("c2"))
                                .Feature("cx4").EqualTo(cx4 => cx4.Symbol("d2", "d3")).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol("a2"))
                                .Feature("cx2").EqualTo(cx2 => cx2.Symbol("b1"))
                                .Feature("cx3").EqualTo(cx2 => cx2.Symbol("c2"))
                                .Feature("cx4").EqualTo(cx4 => cx4.Symbol("d1", "d2")).Value,

                                // re-entrant
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1.Symbol("a2"))
                                .Feature("cx2").ReferringTo(1).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx2").EqualTo(1, cx2 => cx2.Symbol("a1", "a3"))
                                .Feature("cx1").ReferringTo(1).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx2").EqualTo(cx2 => cx2.Symbol(1, "a1", "a3"))
                                .Feature("cx1").EqualTo(cx1 => cx1.Feature("a").ReferringTo(1)).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1.Symbol("a1", "a2"))
                                .Feature("cx2").ReferringTo(1).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1.Symbol("a2", "a3", "a4"))
                                .Feature("cx2").ReferringTo(1).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx2").EqualTo(cx2 => cx2.Symbol(1, "a2", "a3", "a4"))
                                .Feature("cx1").EqualTo(cx1 => cx1.Feature("a").ReferringTo(1)).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx2").EqualTo(1, cx2 => cx2.Symbol("a3"))
                                .Feature("cx1").ReferringTo(1).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx2").EqualTo(1, cx2 => cx2.Symbol("a2", "a3", "a4"))
                                .Feature("cx1").ReferringTo(1).Value,

                                // cyclic
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                                             .Symbol("a2").Symbol("b1").Feature("cx2").ReferringTo(1)).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                                             .Symbol("a2").Symbol("b2").Feature("cx2").ReferringTo(1)).Value,
                                // fs1 is not re-entrant and fs2 is re-entrant on cx2, so fs2 wins out and replaces fs1's value for cx2
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                                             .Symbol("a2").Symbol("b1").Feature("cx2").ReferringTo(1)).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                                             .Symbol("a2").Symbol("b1").Symbol("c2").Feature("cx2").ReferringTo(1)).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                                             .Symbol("a2").Symbol("b1").Symbol("c2").Feature("cx2").ReferringTo(1)).Value,

                                // variable
                                featSys => FeatureStruct.New(featSys).Feature("a").Not.EqualToVariable("var1").Symbol("b-").Value,
                                featSys => FeatureStruct.New(featSys).Symbol("a+").Symbol("b-").Value,
                                featSys => FeatureStruct.New(featSys).Feature("a").Not.EqualToVariable("var1").Symbol("b-").Value,
                                featSys => FeatureStruct.New(featSys).Symbol("a+").Symbol("b-").Value,
                                featSys => FeatureStruct.New(featSys).Symbol("a-").Symbol("b-").Value);
        }
Ejemplo n.º 2
0
        private void TestBinaryOperation <TResult>(IEqualityComparer <TResult> comparer, Func <FeatureStruct, FeatureStruct, TResult> resultsSelector,
                                                   Func <FeatureStruct, FeatureStruct, VariableBindings, TResult> varResultsSelector, params Func <FeatureSystem, TResult>[] expectedSelectors)
        {
            // simple
            var featSys = new FeatureSystem
            {
                new SymbolicFeature("a", new FeatureSymbol("a1"), new FeatureSymbol("a2"), new FeatureSymbol("a3")),
                new SymbolicFeature("b", new FeatureSymbol("b1"), new FeatureSymbol("b2"), new FeatureSymbol("b3")),
                new SymbolicFeature("c", new FeatureSymbol("c1"), new FeatureSymbol("c2"), new FeatureSymbol("c3"))
            };

            featSys.Freeze();

            FeatureStruct fs1 = FeatureStruct.NewMutable(featSys).Symbol("a1").Symbol("b1").Value;
            FeatureStruct fs2 = FeatureStruct.NewMutable(featSys).Symbol("a2").Symbol("c2").Value;

            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[0](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Symbol("a1", "a2").Symbol("b1").Symbol("c2").Value;
            fs2 = FeatureStruct.NewMutable(featSys).Symbol("a2").Symbol("c2").Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[1](featSys)).Using(comparer));

            // complex
            featSys = new FeatureSystem
            {
                new ComplexFeature("cx1"),
                new SymbolicFeature("a", new FeatureSymbol("a1"), new FeatureSymbol("a2"), new FeatureSymbol("a3")),
                new ComplexFeature("cx2"),
                new SymbolicFeature("b", new FeatureSymbol("b1"), new FeatureSymbol("b2"), new FeatureSymbol("b3")),
                new ComplexFeature("cx3"),
                new SymbolicFeature("c", new FeatureSymbol("c1"), new FeatureSymbol("c2"), new FeatureSymbol("c3")),
                new ComplexFeature("cx4"),
                new SymbolicFeature("d", new FeatureSymbol("d1"), new FeatureSymbol("d2"), new FeatureSymbol("d3"))
            };
            featSys.Freeze();

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol("a1"))
                  .Feature("cx2").EqualTo(cx2 => cx2.Symbol("b1"))
                  .Feature("cx4").EqualTo(cx4 => cx4.Symbol("d1")).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol("a2"))
                  .Feature("cx3").EqualTo(cx2 => cx2.Symbol("c2"))
                  .Feature("cx4").EqualTo(cx4 => cx4.Symbol("d2", "d3")).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[2](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol("a1", "a2"))
                  .Feature("cx2").EqualTo(cx2 => cx2.Symbol("b1"))
                  .Feature("cx4").EqualTo(cx4 => cx4.Symbol("d1")).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol("a2"))
                  .Feature("cx3").EqualTo(cx2 => cx2.Symbol("c2"))
                  .Feature("cx4").EqualTo(cx4 => cx4.Symbol("d1", "d2")).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[3](featSys)).Using(comparer));

            // re-entrant
            featSys = new FeatureSystem
            {
                new ComplexFeature("cx1"),
                new SymbolicFeature("a", new FeatureSymbol("a1"), new FeatureSymbol("a2"), new FeatureSymbol("a3"), new FeatureSymbol("a4")),
                new ComplexFeature("cx2")
            };
            featSys.Freeze();

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(1, cx1 => cx1.Symbol("a1"))
                  .Feature("cx2").ReferringTo(1).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx2").EqualTo(cx2 => cx2.Symbol("a2")).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[4](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol("a1", "a2")).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx2").EqualTo(1, cx2 => cx2.Symbol("a1", "a3"))
                  .Feature("cx1").ReferringTo(1).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[5](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol("a1", "a2")).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx2").EqualTo(cx2 => cx2.Symbol(1, "a1", "a3"))
                  .Feature("cx1").EqualTo(cx1 => cx1.Feature("a").ReferringTo(1)).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[6](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(1, cx1 => cx1.Symbol("a1"))
                  .Feature("cx2").ReferringTo(1).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx2").EqualTo(1, cx2 => cx2.Symbol("a1", "a2"))
                  .Feature("cx1").ReferringTo(1).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[7](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(1, cx1 => cx1.Symbol("a1", "a2"))
                  .Feature("cx2").ReferringTo(1).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx2").EqualTo(1, cx2 => cx2.Symbol("a2", "a3", "a4"))
                  .Feature("cx1").ReferringTo(1).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[8](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol(1, "a1", "a2"))
                  .Feature("cx2").EqualTo(cx2 => cx2.Feature("a").ReferringTo(1)).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx2").EqualTo(cx2 => cx2.Symbol(1, "a2", "a3", "a4"))
                  .Feature("cx1").EqualTo(cx1 => cx1.Feature("a").ReferringTo(1)).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[9](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol("a1", "a2")).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx2").EqualTo(1, cx2 => cx2.Symbol("a3"))
                  .Feature("cx1").ReferringTo(1).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[10](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(1, cx1 => cx1.Symbol("a1"))
                  .Feature("cx2").ReferringTo(1).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx2").EqualTo(1, cx2 => cx2.Symbol("a2", "a3", "a4"))
                  .Feature("cx1").ReferringTo(1).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[11](featSys)).Using(comparer));

            // cyclic
            featSys = new FeatureSystem
            {
                new ComplexFeature("cx1"),
                new SymbolicFeature("a", new FeatureSymbol("a1"), new FeatureSymbol("a2"), new FeatureSymbol("a3")),
                new SymbolicFeature("b", new FeatureSymbol("b1"), new FeatureSymbol("b2"), new FeatureSymbol("b3")),
                new SymbolicFeature("c", new FeatureSymbol("c1"), new FeatureSymbol("c2"), new FeatureSymbol("c3")),
                new ComplexFeature("cx2")
            };
            featSys.Freeze();

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(cx1 => cx1
                                                                           .Symbol("a1").Symbol("b1")).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                           .Symbol("a2").Feature("cx2").ReferringTo(1)).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[12](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                           .Symbol("a1", "a2").Feature("cx2").ReferringTo(1)).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(cx1 => cx1
                                                                           .Symbol("a2").Symbol("b2")).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[13](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(cx1 => cx1
                                                                           .Symbol("a1", "a2").Symbol("b1").Feature("cx2").EqualTo(cx2 => cx2.Symbol("c1"))).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                           .Symbol("a2").Feature("cx2").ReferringTo(1)).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[14](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(cx1 => cx1
                                                                           .Symbol("a1").Symbol("b1").Feature("cx2").EqualTo(cx2 => cx2.Symbol("c1", "c2"))).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                           .Symbol("a2").Symbol("c2").Feature("cx2").ReferringTo(1)).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[15](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                           .Symbol("a1").Symbol("b1").Symbol("c1").Feature("cx2").ReferringTo(1)).Value;
            fs2 = FeatureStruct.NewMutable(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                           .Symbol("a2").Symbol("c2").Feature("cx2").ReferringTo(1)).Value;
            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[16](featSys)).Using(comparer));

            // variable
            featSys = new FeatureSystem
            {
                new SymbolicFeature("a", new FeatureSymbol("a+", "+"), new FeatureSymbol("a-", "-")),
                new SymbolicFeature("b", new FeatureSymbol("b+", "+"), new FeatureSymbol("b-", "-"))
            };
            featSys.Freeze();

            fs1 = FeatureStruct.NewMutable(featSys)
                  .Feature("a").EqualToVariable("var1")
                  .Symbol("b-").Value;

            fs2 = FeatureStruct.NewMutable(featSys)
                  .Feature("a").Not.EqualToVariable("var1")
                  .Symbol("b-").Value;

            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[17](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys)
                  .Feature("a").EqualToVariable("var1")
                  .Symbol("b-").Value;

            fs2 = FeatureStruct.NewMutable(featSys)
                  .Symbol("a+")
                  .Symbol("b-").Value;

            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[18](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys)
                  .Symbol("a+")
                  .Symbol("b-").Value;

            fs2 = FeatureStruct.NewMutable(featSys)
                  .Feature("a").Not.EqualToVariable("var1")
                  .Symbol("b-").Value;

            Assert.That(resultsSelector(fs1, fs2), Is.EqualTo(expectedSelectors[19](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys)
                  .Symbol("a+")
                  .Symbol("b-").Value;

            fs2 = FeatureStruct.NewMutable(featSys)
                  .Feature("a").Not.EqualToVariable("var1")
                  .Symbol("b-").Value;

            var varBindings = new VariableBindings();

            varBindings["var1"] = new SymbolicFeatureValue(featSys.GetSymbol("a-"));
            Assert.That(varResultsSelector(fs1, fs2, varBindings), Is.EqualTo(expectedSelectors[20](featSys)).Using(comparer));

            fs1 = FeatureStruct.NewMutable(featSys)
                  .Symbol("a+")
                  .Symbol("b-").Value;

            fs2 = FeatureStruct.NewMutable(featSys)
                  .Feature("a").Not.EqualToVariable("var1")
                  .Symbol("b-").Value;

            varBindings         = new VariableBindings();
            varBindings["var1"] = new SymbolicFeatureValue(featSys.GetSymbol("a+"));
            Assert.That(varResultsSelector(fs1, fs2, varBindings), Is.EqualTo(expectedSelectors[21](featSys)).Using(comparer));
        }
Ejemplo n.º 3
0
        public void Unify()
        {
            Func <FeatureStruct, FeatureStruct, FeatureStruct> resultsSelector = (fs1, fs2) =>
            {
                FeatureStruct res;
                return(fs1.Unify(fs2, out res) ? res : null);
            };
            Func <FeatureStruct, FeatureStruct, VariableBindings, FeatureStruct> varResultsSelector = (fs1, fs2, varBindings) =>
            {
                FeatureStruct res;
                return(fs1.Unify(fs2, varBindings, out res) ? res : null);
            };

            TestBinaryOperation(FreezableEqualityComparer <FeatureStruct> .Default, resultsSelector, varResultsSelector,
                                // simple
                                featSys => null,
                                featSys => FeatureStruct.New(featSys).Symbol("a2").Symbol("b1").Symbol("c2").Value,

                                // complex
                                featSys => null,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol("a2"))
                                .Feature("cx2").EqualTo(cx2 => cx2.Symbol("b1"))
                                .Feature("cx3").EqualTo(cx2 => cx2.Symbol("c2"))
                                .Feature("cx4").EqualTo(cx4 => cx4.Symbol("d1")).Value,

                                // re-entrant
                                featSys => null,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1.Symbol("a1"))
                                .Feature("cx2").ReferringTo(1).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol(1, "a1"))
                                .Feature("cx2").EqualTo(cx2 => cx2.Feature("a").ReferringTo(1)).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1.Symbol("a1"))
                                .Feature("cx2").ReferringTo(1).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1.Symbol("a2"))
                                .Feature("cx2").ReferringTo(1).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(cx1 => cx1.Symbol(1, "a2"))
                                .Feature("cx2").EqualTo(cx2 => cx2.Feature("a").ReferringTo(1)).Value,
                                featSys => null,
                                featSys => null,

                                // cyclic
                                featSys => null,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                                             .Symbol("a2").Symbol("b2").Feature("cx2").ReferringTo(1)).Value,
                                featSys => FeatureStruct.New(featSys).Feature("cx1").EqualTo(1, cx1 => cx1
                                                                                             .Symbol("a2").Symbol("b1").Symbol("c1").Feature("cx2").ReferringTo(1)).Value,
                                featSys => null,
                                featSys => null,

                                // variable
                                featSys => null,
                                featSys => FeatureStruct.New(featSys).Symbol("a+").Symbol("b-").Value,
                                featSys => FeatureStruct.New(featSys).Symbol("a+").Symbol("b-").Value,
                                featSys => FeatureStruct.New(featSys).Symbol("a+").Symbol("b-").Value,
                                featSys => null);

            var featureSystem = new FeatureSystem
            {
                new ComplexFeature("a"),
                new SymbolicFeature("b", new FeatureSymbol("c")),
                new ComplexFeature("d"),
                new SymbolicFeature("e", new FeatureSymbol("f")),
                new ComplexFeature("g"),
                new SymbolicFeature("h", new FeatureSymbol("j"))
            };

            FeatureStruct featStruct1 = FeatureStruct.New(featureSystem)
                                        .Feature("a").EqualTo(a => a
                                                              .Feature("b").EqualTo("c"))
                                        .Feature("d").EqualTo(1, d => d
                                                              .Feature("e").EqualTo("f"))
                                        .Feature("g").ReferringTo(1).Value;

            FeatureStruct featStruct2 = FeatureStruct.New(featureSystem)
                                        .Feature("a").EqualTo(1, a => a
                                                              .Feature("b").EqualTo("c"))
                                        .Feature("d").ReferringTo(1)
                                        .Feature("g").EqualTo(g => g
                                                              .Feature("h").EqualTo("j")).Value;

            FeatureStruct result;

            Assert.IsTrue(featStruct1.Unify(featStruct2, out result));

            featureSystem = new FeatureSystem
            {
                new ComplexFeature("a"),
                new SymbolicFeature("b", new FeatureSymbol("c")),
                new ComplexFeature("d"),
                new SymbolicFeature("e", new FeatureSymbol("f")),
                new ComplexFeature("g"),
                new SymbolicFeature("h", new FeatureSymbol("j")),
                new ComplexFeature("i")
            };

            featStruct1 = FeatureStruct.New(featureSystem)
                          .Feature("a").EqualTo(1, a => a
                                                .Feature("b").EqualTo("c"))
                          .Feature("d").EqualTo(2, d => d
                                                .Feature("e").EqualTo("f"))
                          .Feature("g").ReferringTo(2)
                          .Feature("i").ReferringTo(1).Value;

            featStruct2 = FeatureStruct.New(featureSystem)
                          .Feature("a").EqualTo(1, a => a
                                                .Feature("b").EqualTo("c"))
                          .Feature("d").EqualTo(g => g
                                                .Feature("h").EqualTo("j"))
                          .Feature("g").ReferringTo(1).Value;

            Assert.That(featStruct1.Unify(featStruct2, out result), Is.True);
            Assert.That(result, Is.EqualTo(FeatureStruct.New(featureSystem)
                                           .Feature("a").EqualTo(1, a => a
                                                                 .Feature("b").EqualTo("c")
                                                                 .Feature("e").EqualTo("f")
                                                                 .Feature("h").EqualTo("j"))
                                           .Feature("d").ReferringTo(1)
                                           .Feature("g").ReferringTo(1)
                                           .Feature("i").ReferringTo(1).Value).Using(FreezableEqualityComparer <FeatureStruct> .Default));
        }