Trying a simple fix for issue-619. During debugging, I found that Ana…

…lyticalEquationSolver.Solve( "{-(x + -1000) / (-1)}", "{x}" ) was returning "{{ } \/ { 1000 } \ { }}". That wasn't being interpreted as a FiniteSet. Getting InnerSimplified results in "{1000}", and that fits the FiniteSet type.

Sources/AngouriMath/AngouriMath/Functions/Continuous/Solvers/EquationSolver.cs

@@ -77,7 +77,7 @@ internal static List<List<Entity>> InSolveSystem(List<Entity> equations, ReadOnl
         {
             var var = vars[^1];
             if (equations.Count == 1)
-                return equations[0].InnerSimplified.SolveEquation(var) is FiniteSet els 
+                return equations[0].InnerSimplified.SolveEquation(var).InnerSimplified is FiniteSet els 
                        ? els.Select(sol => new List<Entity> { sol }).ToList()
                        : new();
             var result = new List<List<Entity>>();

Sources/Tests/UnitTests/Algebra/SolveTest/SolveSystem.cs

@@ -102,5 +102,24 @@ public void EquationWithDivisionIsSolved() => AssertSystemSolvable(new Entity[]
             "x2 + y",
             "y - x - 3"
         }, new Entity.Variable[] { "x", "y" }, 2);
+
+
+        [Fact]
+        public void SystemWithZero() => AssertSystemSolvable(new Entity[] {
+            "x - y - 1000",
+            "y - 0"
+        }, new Entity.Variable[] { "x", "y" }, 1);
+
+        [Fact]
+        public void SystemWithZero2() => AssertSystemSolvable(new Entity[] {
+            "y - 0",
+            "x - y - 1000"            
+        }, new Entity.Variable[] { "x", "y" }, 1);
+
+        [Fact]
+        public void SystemWithZero3() => AssertSystemSolvable(new Entity[] {
+            "y - 0",
+            "x - y"
+        }, new Entity.Variable[] { "x", "y" }, 1);
     }
 }