diff --git a/Steepfile b/Steepfile
index 6e455bbe..a8789d38 100644
--- a/Steepfile
+++ b/Steepfile
@@ -11,12 +11,14 @@ target :lib do
   check "lib/lrama/grammar/error_token.rb"
   check "lib/lrama/grammar/parameterizing_rule"
   check "lib/lrama/grammar/parameterizing_rules"
+  check "lib/lrama/grammar/symbols"
   check "lib/lrama/grammar/percent_code.rb"
   check "lib/lrama/grammar/precedence.rb"
   check "lib/lrama/grammar/printer.rb"
   check "lib/lrama/grammar/reference.rb"
   check "lib/lrama/grammar/rule_builder.rb"
   check "lib/lrama/grammar/symbol.rb"
+  check "lib/lrama/grammar/type.rb"
   check "lib/lrama/lexer"
   check "lib/lrama/report"
   check "lib/lrama/bitmap.rb"
diff --git a/lib/lrama/grammar/symbols/resolver.rb b/lib/lrama/grammar/symbols/resolver.rb
index 456993b8..07e03e70 100644
--- a/lib/lrama/grammar/symbols/resolver.rb
+++ b/lib/lrama/grammar/symbols/resolver.rb
@@ -14,7 +14,7 @@ def symbols
         end
 
         def sort_by_number!
-          @symbols.sort_by!(&:number)
+          symbols.sort_by!(&:number)
         end
 
         def add_term(id:, alias_name: nil, tag: nil, token_id: nil, replace: false)
@@ -198,9 +198,17 @@ def fill_terms_number
                 when "\\\\"
                   sym.token_id = 92
                 when /\A\\(\d+)\z/
-                  sym.token_id = Integer($1, 8)
+                  unless (id = Integer($1, 8)).nil?
+                    sym.token_id = id
+                  else
+                    raise "Unknown Char s_value #{sym}"
+                  end
                 when /\A(.)\z/
-                  sym.token_id = $1.bytes.first
+                  unless (id = $1&.bytes&.first).nil?
+                    sym.token_id = id
+                  else
+                    raise "Unknown Char s_value #{sym}"
+                  end
                 else
                   raise "Unknown Char s_value #{sym}"
                 end
@@ -237,7 +245,7 @@ def used_numbers
           return @used_numbers if defined?(@used_numbers)
 
           @used_numbers = {}
-          @symbols.map(&:number).each do |n|
+          symbols.map(&:number).each do |n|
             @used_numbers[n] = true
           end
           @used_numbers
diff --git a/sig/lrama/grammar/symbol.rbs b/sig/lrama/grammar/symbol.rbs
index 6c345bdb..0d066934 100644
--- a/sig/lrama/grammar/symbol.rbs
+++ b/sig/lrama/grammar/symbol.rbs
@@ -2,7 +2,7 @@ module Lrama
   class Grammar
     class Symbol
       attr_accessor id: Lexer::Token
-      attr_accessor alias_name: String
+      attr_accessor alias_name: String?
       attr_accessor number: Integer
       attr_accessor tag: Lexer::Token?
       attr_accessor term: bool
@@ -20,8 +20,8 @@ module Lrama
       attr_writer accept_symbol: Symbol
 
       def initialize: (
-          id: Lexer::Token, alias_name: String?, number: Integer?, tag: Lexer::Token?,
-          term: bool, token_id: Integer?, nullable: bool?, precedence: Precedence?, printer: Printer?) -> void
+          id: Lexer::Token, term: bool, ?alias_name: String?, ?number: Integer?, ?tag: Lexer::Token?,
+          ?token_id: Integer?, ?nullable: bool?, ?precedence: Precedence?, ?printer: Printer?) -> void
 
       def term?: () -> bool
       def nterm?: () -> bool
@@ -31,7 +31,7 @@ module Lrama
       def accept_symbol?: () -> bool
       def display_name: () -> String
       def enum_name: () -> String
-      def comment: () -> String
+      def comment: () -> String?
     end
   end
 end
diff --git a/sig/lrama/grammar/symbols/resolver.rbs b/sig/lrama/grammar/symbols/resolver.rbs
new file mode 100644
index 00000000..8f16cd16
--- /dev/null
+++ b/sig/lrama/grammar/symbols/resolver.rbs
@@ -0,0 +1,41 @@
+module Lrama
+  class Grammar
+    class Symbols
+      class Resolver
+        attr_reader terms: Array[Grammar::Symbol]
+        attr_reader nterms: Array[Grammar::Symbol]
+
+        @symbols: Array[Grammar::Symbol]?
+        @number: Integer
+        @used_numbers: Hash[Integer, bool]
+
+        def initialize: () -> void
+        def symbols: () -> Array[Grammar::Symbol]
+        def sort_by_number!: () -> void
+        def add_term: (id: Lexer::Token, ?alias_name: String?, ?tag: Lexer::Token?, ?token_id: Integer?, ?replace: bool) -> Grammar::Symbol
+        def add_nterm: (id: Lexer::Token, ?alias_name: String?, ?tag: Lexer::Token?) -> Grammar::Symbol?
+        def find_symbol_by_s_value: (Grammar::Symbol s_value) -> Grammar::Symbol?
+        def find_symbol_by_s_value!: (Grammar::Symbol s_value) -> Grammar::Symbol
+        def find_symbol_by_id: (Lexer::Token id) -> Grammar::Symbol?
+        def find_symbol_by_id!: (Lexer::Token id) -> Grammar::Symbol
+        def find_symbol_by_token_id: (Integer token_id) -> Grammar::Symbol?
+        def find_symbol_by_number!: (Integer number) -> Grammar::Symbol
+        def fill_symbol_number: () -> void
+        def fill_nterm_type: (Array[Grammar::Type] types) -> void
+        def fill_printer: (Array[Grammar::Printer] printers) -> void
+        def fill_error_token: (Array[Grammar::ErrorToken] error_tokens) -> void
+        def token_to_symbol: (Lexer::Token token) -> Grammar::Symbol
+        def validate!: () -> void
+
+        private
+
+        def find_nterm_by_id!: (Lexer::Token id) -> Grammar::Symbol
+        def fill_terms_number: () -> void
+        def fill_nterms_number: () -> void
+        def used_numbers: () -> Hash[Integer, bool]
+        def validate_number_uniqueness!: () -> void
+        def validate_alias_name_uniqueness!: () -> void
+      end
+    end
+  end
+end
diff --git a/sig/lrama/grammar/type.rbs b/sig/lrama/grammar/type.rbs
new file mode 100644
index 00000000..2cdd8b13
--- /dev/null
+++ b/sig/lrama/grammar/type.rbs
@@ -0,0 +1,11 @@
+module Lrama
+  class Grammar
+    class Type
+      attr_reader id: Lexer::Token
+      attr_reader tag: Lexer::Token
+
+      def initialize: (id: Lexer::Token, tag: Lexer::Token) -> void
+      def ==: (Grammar::Type other) -> bool
+    end
+  end
+end