diff --git a/src/function/ArgumentValidator.java b/src/function/ArgumentValidator.java
index f12951c..1460783 100644
--- a/src/function/ArgumentValidator.java
+++ b/src/function/ArgumentValidator.java
@@ -124,16 +124,16 @@ public class ArgumentValidator {
 
         private static final long serialVersionUID = 1L;
         private String functionName;
-        private Cons originalSExpression;
+        private Cons argumentList;
 
         public TooFewArgumentsException(String functionName, Cons argumentList) {
             this.functionName = functionName;
-            this.originalSExpression = new Cons(new Symbol(this.functionName), argumentList);
+            this.argumentList = argumentList;
         }
 
         @Override
         public String getMessage() {
-            return MessageFormat.format("too few arguments given to {0}: {1}", functionName, originalSExpression);
+            return MessageFormat.format("too few arguments given to {0}: {1}", functionName, argumentList);
         }
     }
 
@@ -141,16 +141,16 @@ public class ArgumentValidator {
 
         private static final long serialVersionUID = 1L;
         private String functionName;
-        private Cons originalSExpression;
+        private Cons argumentList;
 
         public TooManyArgumentsException(String functionName, Cons argumentList) {
             this.functionName = functionName;
-            this.originalSExpression = new Cons(new Symbol(this.functionName), argumentList);
+            this.argumentList = argumentList;
         }
 
         @Override
         public String getMessage() {
-            return MessageFormat.format("too many arguments given to {0}: {1}", functionName, originalSExpression);
+            return MessageFormat.format("too many arguments given to {0}: {1}", functionName, argumentList);
         }
     }
 
@@ -158,16 +158,16 @@ public class ArgumentValidator {
 
         private static final long serialVersionUID = 1L;
         private String functionName;
-        private Cons originalSExpression;
+        private Cons argumentList;
 
         public DottedArgumentListException(String functionName, Cons argumentList) {
             this.functionName = functionName;
-            this.originalSExpression = new Cons(new Symbol(this.functionName), argumentList);
+            this.argumentList = argumentList;
         }
 
         @Override
         public String getMessage() {
-            return MessageFormat.format("dotted argument list given to {0}: {1}", functionName, originalSExpression);
+            return MessageFormat.format("dotted argument list given to {0}: {1}", functionName, argumentList);
         }
     }
 
diff --git a/src/function/UserDefinedFunction.java b/src/function/UserDefinedFunction.java
index 9623c45..525a803 100644
--- a/src/function/UserDefinedFunction.java
+++ b/src/function/UserDefinedFunction.java
@@ -12,7 +12,7 @@ public class UserDefinedFunction extends LispFunction {
     private Cons body;
     private Cons lambdaExpression;
     private ExecutionContext executionContext;
-    private SymbolTable scope;
+    private SymbolTable functionScope;
     private ArrayList<String> formalParameters;
     private ArgumentValidator argumentValidator;
 
@@ -21,7 +21,7 @@ public class UserDefinedFunction extends LispFunction {
         this.body = body;
         this.lambdaExpression = new Cons(new Symbol(name), new Cons(lambdaList, body));
         this.executionContext = ExecutionContext.getInstance();
-        this.scope = executionContext.getScope();
+        this.functionScope = executionContext.getScope();
 
         for (this.formalParameters = new ArrayList<>(); lambdaList.consp(); lambdaList = (Cons) lambdaList.getCdr())
             this.formalParameters.add(lambdaList.getCar().toString());
@@ -33,49 +33,33 @@ public class UserDefinedFunction extends LispFunction {
     public SExpression call(Cons argumentList) {
         argumentValidator.validate(argumentList);
 
-        // bind the values of the arguments to the formal parameter names
         bindParameterValues(argumentList);
-
-        // store the environment of the S-expression that called this function
-        // (the current environment)
         SymbolTable callingScope = executionContext.getScope();
+        executionContext.setScope(functionScope);
 
-        // replace the current environment with the environment of this
-        // function
-        executionContext.setScope(scope);
+        SExpression lastEvaluation = null;
 
-        Cons currentSExpression = body;
-        SExpression lastValue = null;
+        for (Cons expression = body; expression.consp(); expression = (Cons) expression.getCdr())
+            lastEvaluation = EVAL.eval(expression.getCar());
 
-        // evaluate all the S-expressions making up this function's body
-        while (currentSExpression.consp()) {
-            lastValue = EVAL.eval(currentSExpression.getCar());
-            currentSExpression = (Cons) currentSExpression.getCdr();
-        }
-
-        // replace the environment of the S-expression that called this
-        // function
         executionContext.setScope(callingScope);
-
-        // remove the bindings of the arguments to the formal parameter names
-        // in the environment of this function
         releaseParameterValues();
 
-        return lastValue;
+        return lastEvaluation;
     }
 
     private void bindParameterValues(Cons argumentList) {
-        scope = new SymbolTable(scope);
+        functionScope = new SymbolTable(functionScope);
 
         for (String parameter : formalParameters) {
             SExpression currentArg = argumentList.getCar();
-            scope.put(parameter, currentArg);
+            functionScope.put(parameter, currentArg);
             argumentList = (Cons) argumentList.getCdr();
         }
     }
 
     private void releaseParameterValues() {
-        scope = new SymbolTable(scope.getParent());
+        functionScope = new SymbolTable(functionScope.getParent());
     }
 
     public Cons getLambdaExpression() {
diff --git a/src/function/builtin/special/DEFUN.java b/src/function/builtin/special/DEFUN.java
index afbcf36..2e0b7b3 100644
--- a/src/function/builtin/special/DEFUN.java
+++ b/src/function/builtin/special/DEFUN.java
@@ -20,10 +20,10 @@ public class DEFUN extends LispFunction {
         this.argumentValidator.setMinimumNumberOfArguments(3);
         this.argumentValidator.setFirstArgumentExpectedType(Symbol.class);
 
-        this.lambdaListIsListValidator = new ArgumentValidator("DEFUN|lambda_list|");
+        this.lambdaListIsListValidator = new ArgumentValidator("DEFUN|lambda-list|");
         this.lambdaListIsListValidator.setEveryArgumentExpectedType(Cons.class);
 
-        this.lambdaListValidator = new ArgumentValidator("DEFUN|lambda_list|");
+        this.lambdaListValidator = new ArgumentValidator("DEFUN|parameter|");
         this.lambdaListValidator.setEveryArgumentExpectedType(Symbol.class);
 
         this.environment = Environment.getInstance();
diff --git a/src/function/builtin/special/LAMBDA.java b/src/function/builtin/special/LAMBDA.java
index 74b0230..384ba93 100644
--- a/src/function/builtin/special/LAMBDA.java
+++ b/src/function/builtin/special/LAMBDA.java
@@ -19,7 +19,7 @@ public class LAMBDA extends LispFunction {
     public static UserDefinedFunction createFunction(Cons lambdaExpression) {
         SExpression cdr = lambdaExpression.getCdr();
 
-        ArgumentValidator lambdaValidator = new ArgumentValidator(":LAMBDA");
+        ArgumentValidator lambdaValidator = new ArgumentValidator("LAMBDA|create|");
         lambdaValidator.setEveryArgumentExpectedType(Cons.class);
         lambdaValidator.validate(LIST.makeList(cdr));
 
@@ -29,11 +29,15 @@ public class LAMBDA extends LispFunction {
     }
 
     private ArgumentValidator argumentValidator;
+    private ArgumentValidator lambdaListValidator;
 
     public LAMBDA() {
         this.argumentValidator = new ArgumentValidator("LAMBDA");
         this.argumentValidator.setFirstArgumentExpectedType(Cons.class);
         this.argumentValidator.setMinimumNumberOfArguments(2);
+
+        this.lambdaListValidator = new ArgumentValidator("LAMBDA|lambda-list|");
+        this.lambdaListValidator.setEveryArgumentExpectedType(Symbol.class);
     }
 
     public LambdaExpression call(Cons argumentList) {
@@ -43,6 +47,8 @@ public class LAMBDA extends LispFunction {
         Cons lambdaList = (Cons) car;
         Cons body = (Cons) argumentList.getCdr();
 
+        lambdaListValidator.validate(lambdaList);
+
         UserDefinedFunction function = new UserDefinedFunction(":LAMBDA", lambdaList, body);
 
         return new LambdaExpression(makeOriginalLambdaExpression(argumentList), function);
diff --git a/src/function/builtin/special/LET.java b/src/function/builtin/special/LET.java
index 302b1bd..ef4f9b4 100644
--- a/src/function/builtin/special/LET.java
+++ b/src/function/builtin/special/LET.java
@@ -8,13 +8,22 @@ import table.*;
 public class LET extends LispFunction {
 
     private ArgumentValidator argumentValidator;
+    private ArgumentValidator variableDefinitionListValidator;
+    private ArgumentValidator pairValidator;
     private ExecutionContext executionContext;
-    private SymbolTable localScope;
 
     public LET() {
         this.argumentValidator = new ArgumentValidator("LET");
         this.argumentValidator.setMinimumNumberOfArguments(1);
         this.argumentValidator.setFirstArgumentExpectedType(Cons.class);
+
+        this.variableDefinitionListValidator = new ArgumentValidator("LET|pair-list|");
+        this.variableDefinitionListValidator.setEveryArgumentExpectedType(Cons.class);
+
+        this.pairValidator = new ArgumentValidator("LET|pair|");
+        this.pairValidator.setExactNumberOfArguments(2);
+        this.pairValidator.setFirstArgumentExpectedType(Symbol.class);
+
         this.executionContext = ExecutionContext.getInstance();
     }
 
@@ -27,15 +36,15 @@ public class LET extends LispFunction {
     }
 
     private SExpression evaluateInScope(Cons variableDefinitions, Cons body) {
-        createLocalScope(variableDefinitions);
+        SymbolTable localScope = createLocalScope(variableDefinitions);
         SExpression lastEvaluation = evaluateBody(body);
-        restorePreviousScope();
+        restorePreviousScope(localScope);
 
         return lastEvaluation;
     }
 
     private SymbolTable createLocalScope(Cons variableDefinitions) {
-        localScope = new SymbolTable(executionContext.getScope());
+        SymbolTable localScope = new SymbolTable(executionContext.getScope());
         addVariablesToScope(localScope, variableDefinitions);
         executionContext.setScope(localScope);
 
@@ -43,32 +52,20 @@ public class LET extends LispFunction {
     }
 
     private void addVariablesToScope(SymbolTable scope, Cons variableDefinitions) {
-        validateAllPairsAreLists(variableDefinitions);
-
-        for (; variableDefinitions.consp(); variableDefinitions = (Cons) variableDefinitions.getCdr()) {
-            Cons symbolValuePair = (Cons) variableDefinitions.getCar();
-
-            validatePair(symbolValuePair);
-
-            Cons restOfPair = (Cons) symbolValuePair.getCdr();
-            SExpression symbol = symbolValuePair.getCar();
-            SExpression value = restOfPair.getCar();
-
-            scope.put(symbol.toString(), EVAL.eval(value));
-        }
-    }
-
-    private void validateAllPairsAreLists(Cons variableDefinitions) {
-        ArgumentValidator variableDefinitionListValidator = new ArgumentValidator("LET|argumentList|");
-        variableDefinitionListValidator.setEveryArgumentExpectedType(Cons.class);
         variableDefinitionListValidator.validate(variableDefinitions);
+
+        for (; variableDefinitions.consp(); variableDefinitions = (Cons) variableDefinitions.getCdr())
+            addPairToScope((Cons) variableDefinitions.getCar(), scope);
     }
 
-    private void validatePair(Cons symbolValuePair) {
-        ArgumentValidator pairValidator = new ArgumentValidator("LET|pair|");
-        pairValidator.setExactNumberOfArguments(2);
-        pairValidator.setFirstArgumentExpectedType(Symbol.class);
-        pairValidator.validate((Cons) symbolValuePair);
+    private void addPairToScope(Cons symbolValuePair, SymbolTable scope) {
+        pairValidator.validate(symbolValuePair);
+
+        Cons restOfPair = (Cons) symbolValuePair.getCdr();
+        SExpression symbol = symbolValuePair.getCar();
+        SExpression value = restOfPair.getCar();
+
+        scope.put(symbol.toString(), EVAL.eval(value));
     }
 
     private SExpression evaluateBody(Cons body) {
@@ -80,7 +77,7 @@ public class LET extends LispFunction {
         return lastEvaluation;
     }
 
-    private void restorePreviousScope() {
+    private void restorePreviousScope(SymbolTable localScope) {
         executionContext.setScope(localScope.getParent());
     }
 
diff --git a/test/function/builtin/EVALTester.java b/test/function/builtin/EVALTester.java
index e1f0e78..1e9e77b 100644
--- a/test/function/builtin/EVALTester.java
+++ b/test/function/builtin/EVALTester.java
@@ -37,6 +37,12 @@ public class EVALTester {
         assertSExpressionsMatch(parseString(symbol), EVAL.lookupSymbol(symbol));
     }
 
+    @Test
+    public void testLookupNil() {
+        String symbol = "NIL";
+        assertSExpressionsMatch(parseString(symbol), EVAL.lookupSymbol(symbol));
+    }
+
     @Test
     public void testLookupUndefinedSymbol() {
         assertNull(EVAL.lookupSymbol("undefined"));
diff --git a/test/function/builtin/special/LAMBDATester.java b/test/function/builtin/special/LAMBDATester.java
index 7e29c0e..47885d0 100644
--- a/test/function/builtin/special/LAMBDATester.java
+++ b/test/function/builtin/special/LAMBDATester.java
@@ -46,6 +46,13 @@ public class LAMBDATester {
         evaluateString(input);
     }
 
+    @Test(expected = DottedArgumentListException.class)
+    public void testLambdaWithDottedLambdaList() {
+        String input = "(funcall 'lambda (cons 'a 'b) ())";
+
+        evaluateString(input);
+    }
+
     @Test(expected = DottedArgumentListException.class)
     public void testCreateFunctionWithDottedArgumentList() {
         Cons lambdaExpression = new Cons(new Symbol("LAMBDA"), new Cons(Nil.getInstance(), LispNumber.ONE));
@@ -60,9 +67,38 @@ public class LAMBDATester {
         LAMBDA.createFunction(lambdaExpression);
     }
 
+    @Test(expected = BadArgumentTypeException.class)
+    public void testLambdaWithNonSymbolParameter() {
+        evaluateString("(lambda (1) ())");
+    }
+
     @Test(expected = TooFewArgumentsException.class)
     public void testLambdaWithTooFewArguments() {
         evaluateString("(lambda ())");
     }
 
+    @Test
+    public void anonymousLambdaCall() {
+        String input = "((lambda (x) x) 203)";
+
+        assertSExpressionsMatch(new LispNumber("203"), evaluateString(input));
+    }
+
+    @Test
+    public void anonymousLambdaCallWithMultipleArguments() {
+        String input = "((lambda (x y) (+ x y)) 203 2)";
+
+        assertSExpressionsMatch(new LispNumber("205"), evaluateString(input));
+    }
+
+    @Test(expected = TooFewArgumentsException.class)
+    public void anonymousLambdaCallWithTooFewArguments() {
+        evaluateString("((lambda (x) x))");
+    }
+
+    @Test(expected = TooManyArgumentsException.class)
+    public void anonymousLambdaCallWithTooManyArguments() {
+        evaluateString("((lambda (x y) x) 1 2 3)");
+    }
+
 }
diff --git a/test/function/builtin/special/LETTester.java b/test/function/builtin/special/LETTester.java
index bfc3814..6d1e0ca 100644
--- a/test/function/builtin/special/LETTester.java
+++ b/test/function/builtin/special/LETTester.java
@@ -65,6 +65,17 @@ public class LETTester {
         assertSExpressionsMatch(new LispNumber("2"), evaluateString(input));
     }
 
+    @Test
+    public void nestedLetWithGlobals() {
+        String before = "(setf x 92)";
+        String input = "(let ((x 1)) (let ((y (+ 1 x))) y))";
+        String after = "x";
+
+        assertSExpressionsMatch(new LispNumber("92"), evaluateString(before));
+        assertSExpressionsMatch(new LispNumber("2"), evaluateString(input));
+        assertSExpressionsMatch(new LispNumber("92"), evaluateString(after));
+    }
+
     @Test
     public void alterGlobalVariableFromLet() {
         String before = "(setf x 1)";