diff --git a/assignments/PA3/cool.y b/assignments/PA3/cool.y
index 2760cc9..f2a22a5 100644
--- a/assignments/PA3/cool.y
+++ b/assignments/PA3/cool.y
@@ -159,10 +159,11 @@
     %nonassoc '<' LE '='
     %left '+' '-'
     %left '*' '/'
-    %precedence ISVOID
-    %precedence '~'
-    %precedence '@'
-    %precedence '.'
+    %nonassoc ISVOID
+    %nonassoc '~'
+    %nonassoc '@'
+    %nonassoc '.'
+    %left LETEXPR
     
     
     %%
@@ -188,15 +189,15 @@
     stringtable.add_string(curr_filename)); }
     | CLASS TYPEID INHERITS TYPEID '{' feature_list '}' ';'
     { $$ = class_($2,$4,$6,stringtable.add_string(curr_filename)); }
+    | CLASS TYPEID INHERITS TYPEID '{' '}' ';'
+    { $$ = class_($2,$4,nil_Features(),stringtable.add_string(curr_filename)); }
     ;
     
     /* Feature list may be empty, but no empty features in list. */
-    feature_list:		/* empty */
-    {  $$ = nil_Features(); }
-    | feature ';'
+    feature_list : feature ';'
     { $$ = single_Features($1); }
     | feature_list feature ';'
-    { $$ = append_Classes($1, single_Features($2)); }
+    { $$ = append_Features($1, single_Features($2)); }
     ;
     
     feature : OBJECTID ':' TYPEID 
@@ -206,11 +207,12 @@
     { $$ = attr($1, $3, $5); }
     | OBJECTID '(' formal_list ')' ':' TYPEID '{' expression '}'
     { $$ = method($1, $3, $6, $8); }
+    | OBJECTID '(' ')' ':' TYPEID '{' expression '}'
+    { $$ = method($1, nil_Formals(), $5, $7); }
     ;
     
-    formal_list : /* empty */
-    { $$ = nil_Formals(); }
-    | formal
+    formal_list
+    : formal
     { $$ = single_Formals($1); }
     | formal_list ',' formal /* a little different from classlist */
     { $$ = append_Formals($1, single_Formals($3)); }
@@ -220,17 +222,15 @@
     { $$ = formal($1, $3); }
     ;
 
-    expression_list_comma : /* TODO Perhaps empty expr_list should not be valid? */
-    { $$ = nil_Expressions(); }
-    | expression
+    expression_list_comma
+    : expression
     { $$ = single_Expressions($1); }
     | expression_list_comma ',' expression
     { $$ = append_Expressions($1, single_Expressions($3)); }
     ;
 
-    expression_list_colon : /* TODO Perhaps empty expr_list should not be valid? */
-    { $$ = nil_Expressions(); }
-    | expression ';'
+    expression_list_colon 
+    : expression ';' /* the only usage `{ [[expr; ]]+}` says one or more exprs needed, so no empty option*/
     { $$ = single_Expressions($1); }
     | expression_list_colon expression ';'
     { $$ = append_Expressions($1, single_Expressions($2)); }
@@ -241,23 +241,36 @@
       /* expr[@TYPE].ID([expr[[,expr]]*]) */
     | expression '.' OBJECTID '(' expression_list_comma ')'
     { $$ = dispatch($1, $3, $5); }
+    | expression '.' OBJECTID '(' ')'
+    { $$ = dispatch($1, $3, nil_Expressions()); }
       /* Only in the case of @TYPE, we use static dispatch*/
     | expression '@' TYPEID '.' OBJECTID '(' expression_list_comma ')'
     { $$ = static_dispatch($1, $3, $5, $7); }
+    | expression '@' TYPEID '.' OBJECTID '(' ')'
+    { $$ = static_dispatch($1, $3, $5, nil_Expressions()); }
       /* Actually, `ID( [ expr [[, expr]]∗ ])` is self omitted, so add it in parsing */
     | OBJECTID '(' expression_list_comma ')'
     { $$ = dispatch(object(idtable.add_string("self")), $1, $3); }
+    | OBJECTID '(' ')'
+    { $$ = dispatch(object(idtable.add_string("self")), $1, nil_Expressions()); }
     | IF expression THEN expression ELSE expression FI
     { $$ = cond($2, $4, $6); }
     | WHILE expression LOOP expression POOL
     { $$ = loop($2, $4); }
     | '{' expression_list_colon '}'
     { $$ = block($2); }
-    /* TODO let expr */
     /* [manual-P21, tour-section6.5]
     * The let constructor only allows one identifier.
     * When parsing a let with multiple idents, it should be transformed into nested lets
     */
+    /* It is not any obvious to me where the shift-reduce conflict lies.
+    * Try `bison -Wcounterexample {OTHERFLAGS} cool.y > counterexample.txt 2>&1`
+    * Thanks to the examples, one possible situation could be: let id1:T1 in expression.f()
+    * there could be 2 interpretations: (let id1:T1 in expression).f() | let id1:T1 in (expression.f())
+    * This should be specified to dis-ambiguite
+    *
+    * The manual says, the expr extends as far as possible
+    */
     | LET nested_let
     { $$ = $2; }
     | CASE expression OF case_list ESAC
@@ -265,7 +278,7 @@
     | NEW TYPEID
     { $$ = new_($2); }
     | ISVOID expression
-    { $$ = isvoid($1); }
+    { $$ = isvoid($2); }
     /* the rules below need precedence specification */
     | expression '+' expression
     { $$ = plus($1, $3); }
@@ -276,7 +289,7 @@
     | expression '/' expression
     { $$ = divide($1, $3); }
     | '~' expression
-    { $$ = beg($2); }
+    { $$ = neg($2); }
     | expression '<' expression
     { $$ = lt($1, $3); }
     | expression LE expression
@@ -300,21 +313,23 @@
     case_list : case ';'
     { $$ = single_Cases($1); }
     | case_list case ';'
-    { $$ = append_Casess($1, single_Cases($2)); } 
+    { $$ = append_Cases($1, single_Cases($2)); } 
     ;
     
     case : OBJECTID ':' TYPEID DARROW expression
     { $$ = branch($1, $3, $5); }
     ;
     
-    nested_let: OBJECTID ':' TYPEID ',' nested_let
+    nested_let
+    : OBJECTID ':' TYPEID ',' nested_let 
     { $$ = let($1, $3, no_expr(), $5); }
     | OBJECTID ':' TYPEID ASSIGN expression ',' nested_let
     { $$ = let($1, $3, $5, $7); }
-    | nested_let OBJECTID ':' TYPEID IN expression
-    { $$ = let($2, $4, no_expr(), $6); }
-    | nested_let OBJECTID ':' TYPEID ASSIGN expression IN expression
-    { $$ = let($2, $4, $6, $8); }
+    | OBJECTID ':' TYPEID IN expression %prec LETEXPR
+    { $$ = let($1, $3, no_expr(), $5); }
+    | OBJECTID ':' TYPEID ASSIGN expression IN expression %prec LETEXPR
+    { $$ = let($1, $3, $5, $7); }
+    ;
     /* end of grammar */
     %%