diff --git a/Rakefile b/Rakefile
index edb856f..daf07b1 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,13 +1,15 @@
+# frozen_string_literal: true
+
 require 'rake/testtask'
 
 Rake::TestTask.new do |t|
-  t.pattern = "spec/*_spec.rb"
+  t.pattern = 'spec/*_spec.rb'
 end
 
 task :gem do
-  sh "gem build rpl.gemspec"
+  sh 'gem build rpl.gemspec'
 end
 
 task :run do
-  sh "ruby -Ilib bin/rpl"
+  sh 'ruby -Ilib bin/rpl'
 end
diff --git a/bin/rpl b/bin/rpl
index 8139356..32c183d 100755
--- a/bin/rpl
+++ b/bin/rpl
@@ -78,7 +78,7 @@ class RplRepl
 end
 
 def persistence_filename
-  persistence_dir = ENV['XDG_DATA_HOME']
+  persistence_dir = ENV.fetch('XDG_DATA_HOME', nil)
   persistence_dir ||= '~/.local/share'
   persistence_dir += '/rpl.rb'
 
@@ -88,7 +88,7 @@ end
 options = { run_REPL: false,
             persistence: true,
             live_persistence: true,
-            persistence_filename: persistence_filename,
+            persistence_filename:,
             files: [],
             programs: [],
             verbosity: :critical }
@@ -155,7 +155,7 @@ options[:programs].each do |program|
 end
 
 # third launch REPL if (explicitely or implicitely) asked
-RplRepl.new( interpreter: interpreter ).run! if options[:run_REPL]
+RplRepl.new( interpreter: ).run! if options[:run_REPL]
 
 interpreter.persist_state if options[:persistence]
 
diff --git a/lib/rpl.rb b/lib/rpl.rb
index ec671d1..ef9363a 100644
--- a/lib/rpl.rb
+++ b/lib/rpl.rb
@@ -15,7 +15,7 @@ class Rpl < Interpreter
                   dictionary: Dictionary.new,
                   persistence_filename: nil,
                   live_persistence: true )
-    super( stack: stack, dictionary: dictionary )
+    super( stack:, dictionary: )
 
     @persistence_filename = persistence_filename
     @live_persistence = live_persistence
@@ -37,9 +37,7 @@ class Rpl < Interpreter
   def persist_state
     return if @persistence_filename.nil?
 
-    File.open( @persistence_filename, 'w' ) do |persistence_file|
-      persistence_file.write "#{export_vars}\n#{export_stack}"
-    end
+    File.write(@persistence_filename, "#{export_vars}\n#{export_stack}")
   end
 
   def run!( input )
diff --git a/lib/rpl/dictionary.rb b/lib/rpl/dictionary.rb
index 730026d..c1a49ae 100644
--- a/lib/rpl/dictionary.rb
+++ b/lib/rpl/dictionary.rb
@@ -13,9 +13,9 @@ class Dictionary
 
   def add_word!( names, category, help, implementation )
     names.each do |name|
-      @words[ name ] = { category: category,
-                         help: help,
-                         implementation: implementation }
+      @words[ name ] = { category:,
+                         help:,
+                         implementation: }
     end
   end
 
diff --git a/lib/rpl/parser.rb b/lib/rpl/parser.rb
index 143b876..eeba339 100644
--- a/lib/rpl/parser.rb
+++ b/lib/rpl/parser.rb
@@ -30,7 +30,7 @@ class Parser
                    .join(' ')
     end
 
-    splitted_input = input.split(' ')
+    splitted_input = input.split
 
     # 2-passes:
     # 1. regroup strings, lists, complexes, names and programs
@@ -90,7 +90,7 @@ class Parser
     end
 
     # 2. parse
-    parsed_input = regrouped_input.map do |element|
+    regrouped_input.map do |element|
       if RplBoolean.can_parse?( element )
         Types.new_object( RplBoolean, element )
       elsif RplNumeric.can_parse?( element )
@@ -107,7 +107,5 @@ class Parser
         Types.new_object( RplName, element )
       end
     end
-
-    parsed_input
   end
 end
diff --git a/lib/rpl/types/boolean.rb b/lib/rpl/types/boolean.rb
index ca861fd..78de046 100644
--- a/lib/rpl/types/boolean.rb
+++ b/lib/rpl/types/boolean.rb
@@ -25,7 +25,7 @@ module Types
     end
 
     def ==( other )
-      other.class == RplBoolean and
+      other.class == RplBoolean &&
         other.value == value
     end
   end
diff --git a/lib/rpl/types/complex.rb b/lib/rpl/types/complex.rb
index 026fc7c..8b8d610 100644
--- a/lib/rpl/types/complex.rb
+++ b/lib/rpl/types/complex.rb
@@ -20,20 +20,14 @@ module Types
     end
 
     def self.can_parse?( value )
-      # we systematicalyl trim enclosing ()
-      value = value[1..-2] if value.is_a?( String ) && value[0] == '(' && value[-1] == ')'
+      # we systematically trim enclosing ()
+      value = value[1..-2] if value.is_a?( String ) && (value[0] == '(') && (value[-1] == ')')
 
-      begin
-        Complex( value )
-      rescue ArgumentError
-        return false
-      end
-
-      true
+      !Complex( value, exception: false ).nil?
     end
 
     def ==( other )
-      other.class == RplComplex and
+      other.class == RplComplex &&
         other.value == value
     end
   end
diff --git a/lib/rpl/types/list.rb b/lib/rpl/types/list.rb
index 23e1aeb..5d2840d 100644
--- a/lib/rpl/types/list.rb
+++ b/lib/rpl/types/list.rb
@@ -12,7 +12,7 @@ module Types
       @value = if value.instance_of?( Array )
                  value
                else
-                 # we systematicalyl trim enclosing { }
+                 # we systematically trim enclosing { }
                  Parser.parse( value[2..-3] )
                end
     end
@@ -22,12 +22,13 @@ module Types
     end
 
     def self.can_parse?( value )
-      value.instance_of?( Array ) or
-        value[0..1] == '{ ' && value[-2..] == ' }'
+      value.instance_of?( Array ) ||
+        ( value[0..1] == '{ ' &&
+          value[-2..] == ' }' )
     end
 
     def ==( other )
-      other.class == RplList and
+      other.class == RplList &&
         other.value == value
     end
   end
diff --git a/lib/rpl/types/name.rb b/lib/rpl/types/name.rb
index 445e4d2..8122c71 100644
--- a/lib/rpl/types/name.rb
+++ b/lib/rpl/types/name.rb
@@ -22,14 +22,14 @@ module Types
     end
 
     def self.can_parse?( value )
-      ( value.length > 2 and value[0] == "'" and value[-1] == "'" ) or
-        ( value != "''" and !value.match?(/^[0-9']+$/) and
+      ( value.length > 2 && value[0] == "'" && value[-1] == "'" ) ||
+        ( value != "''" && !value.match?(/^[0-9']+$/) &&
           # it's not any other type
           [RplBoolean, RplList, RplProgram, RplString, RplNumeric].reduce( true ) { |memo, type_class| memo && !type_class.can_parse?( value ) } )
     end
 
     def ==( other )
-      other.class == RplName and
+      other.class == RplName &&
         other.value == value
     end
   end
diff --git a/lib/rpl/types/numeric.rb b/lib/rpl/types/numeric.rb
index d0cde95..8d05e74 100644
--- a/lib/rpl/types/numeric.rb
+++ b/lib/rpl/types/numeric.rb
@@ -32,9 +32,7 @@ module Types
         @base = value.base
       when BigDecimal
         @value = value
-      when Integer
-        @value = BigDecimal( value, @@precision )
-      when Float
+      when Integer, Float
         @value = BigDecimal( value, @@precision )
       when String
         begin
@@ -94,19 +92,19 @@ module Types
     end
 
     def self.can_parse?( value )
-      [RplNumeric, BigDecimal, Integer, Float].include?( value.class ) or
-        ( value.is_a?( String ) and ( value.match?(/^-?[0-9]*\.?[0-9]+$/) or
-                                      value.match?(/^-?∞$/) or
-                                      value.match?(/^0b[0-1]+$/) or
-                                      value.match?(/^0o[0-7]+$/) or
-                                      value.match?(/^0x[0-9a-f]+$/) or
-                                      ( value.match?(/^[0-9]+b[0-9a-z]+$/) and
+      [RplNumeric, BigDecimal, Integer, Float].include?( value.class ) ||
+        ( value.is_a?( String ) && ( value.match?(/^-?[0-9]*\.?[0-9]+$/) ||
+                                      value.match?(/^-?∞$/) ||
+                                      value.match?(/^0b[0-1]+$/) ||
+                                      value.match?(/^0o[0-7]+$/) ||
+                                      value.match?(/^0x[0-9a-f]+$/) ||
+                                      ( value.match?(/^[0-9]+b[0-9a-z]+$/) &&
                                         value.split('_').first.to_i <= 36 ) ) )
     end
 
     def ==( other )
-      other.class == RplNumeric and
-        other.base == base and
+      other.class == RplNumeric &&
+        other.base == base &&
         other.value == value
     end
   end
diff --git a/lib/rpl/types/program.rb b/lib/rpl/types/program.rb
index 5641107..283a36f 100644
--- a/lib/rpl/types/program.rb
+++ b/lib/rpl/types/program.rb
@@ -7,7 +7,7 @@ module Types
     def initialize( value )
       raise RplTypeError unless self.class.can_parse?( value )
 
-      # we systematicalyl trim enclosing « »
+      # we systematically trim enclosing « »
       @value = value[2..-3] # TODO: parse each element ?
     end
 
@@ -16,11 +16,14 @@ module Types
     end
 
     def self.can_parse?( value )
-      value.length > 4 && value[0..1] == '« ' && value[-2..-1] == ' »' && !value[2..-3].strip.empty?
+      value.length > 4 &&
+        value[0..1] == '« ' &&
+        value[-2..] == ' »' &&
+        !value[2..-3].strip.empty?
     end
 
     def ==( other )
-      other.class == RplProgram and
+      other.class == RplProgram &&
         other.value == value
     end
   end
diff --git a/lib/rpl/types/string.rb b/lib/rpl/types/string.rb
index 9318765..d289986 100644
--- a/lib/rpl/types/string.rb
+++ b/lib/rpl/types/string.rb
@@ -22,7 +22,7 @@ module Types
     end
 
     def ==( other )
-      other.class == RplString and
+      other.class == RplString &&
         other.value == value
     end
   end
diff --git a/lib/rpl/words/logarithm.rb b/lib/rpl/words/logarithm.rb
index d184157..084a975 100644
--- a/lib/rpl/words/logarithm.rb
+++ b/lib/rpl/words/logarithm.rb
@@ -10,7 +10,7 @@ module RplLang
 
         category = 'Logs on reals and complexes'
 
-        @dictionary.add_word!( ['ℇ', 'e'],
+        @dictionary.add_word!( %w[ℇ e],
                                category,
                                '( … -- ℇ ) push ℇ',
                                proc do
diff --git a/lib/rpl/words/operations-reals-complexes.rb b/lib/rpl/words/operations-reals-complexes.rb
index b981b33..91e8f87 100644
--- a/lib/rpl/words/operations-reals-complexes.rb
+++ b/lib/rpl/words/operations-reals-complexes.rb
@@ -30,7 +30,7 @@ module RplLang
                                             new_list = if args[1].instance_of?( RplList )
                                                          RplList.new( args[0].to_s ).value.concat( args[1].value )
                                                        else
-                                                         RplList.new( args[0].to_s ).value.concat( [args[1]] )
+                                                         RplList.new( args[0].to_s ).value.push(args[1])
                                                        end
 
                                             RplList.new( "{ #{new_list.join(' ')} }" )
@@ -47,9 +47,9 @@ module RplLang
                                           elsif args[0].instance_of?( RplString )
                                             RplString.new( if args[1].instance_of?( RplString ) ||
                                                               args[1].instance_of?( RplName )
-                                                           "\"#{args[0].value}#{args[1].value}\""
-                                                         else
-                                                           "\"#{args[0].value}#{args[1]}\""
+                                                             "\"#{args[0].value}#{args[1].value}\""
+                                                           else
+                                                             "\"#{args[0].value}#{args[1]}\""
                                                            end )
 
                                           elsif args[0].instance_of?( RplName )
@@ -189,11 +189,11 @@ module RplLang
                                  args = stack_extract( [[RplNumeric]] )
 
                                  @stack << RplNumeric.new( if args[0].value.positive?
-                                                           1
-                                                         elsif args[0].value.negative?
-                                                           -1
-                                                         else
-                                                           0
+                                                             1
+                                                           elsif args[0].value.negative?
+                                                             -1
+                                                           else
+                                                             0
                                                            end )
                                end )
       end
diff --git a/lib/rpl/words/operations-reals.rb b/lib/rpl/words/operations-reals.rb
index 7532eaf..755fbc6 100644
--- a/lib/rpl/words/operations-reals.rb
+++ b/lib/rpl/words/operations-reals.rb
@@ -25,7 +25,7 @@ module RplLang
                                proc do
                                  args = stack_extract( [[RplNumeric], [RplNumeric]] )
 
-                                 @stack << RplNumeric.new( 100.0 * ( args[0].value / args[1].value ), args[1].base )
+                                 @stack << RplNumeric.new( ( args[0].value / args[1].value ) * 100.0, args[1].base )
                                end )
 
         @dictionary.add_word!( ['mod'],
diff --git a/lib/rpl/words/string-list.rb b/lib/rpl/words/string-list.rb
index cdeaa2e..da0c6d6 100644
--- a/lib/rpl/words/string-list.rb
+++ b/lib/rpl/words/string-list.rb
@@ -17,10 +17,10 @@ module RplLang
                                  args = stack_extract( [[RplString, RplList]] )
 
                                  @stack << if args[0].is_a?( RplString )
-                                 Types.new_object( RplString, "\"#{args[0].value.reverse}\"" )
-                               else
-                                 Types.new_object( args[0].class, "{ #{args[0].value.reverse.join(' ')} }" )
-                               end
+                                             Types.new_object( RplString, "\"#{args[0].value.reverse}\"" )
+                                           else
+                                             Types.new_object( args[0].class, "{ #{args[0].value.reverse.join(' ')} }" )
+                                           end
                                end )
       end
     end
diff --git a/lib/rpl/words/time-date.rb b/lib/rpl/words/time-date.rb
index 29afb20..59b2fdd 100644
--- a/lib/rpl/words/time-date.rb
+++ b/lib/rpl/words/time-date.rb
@@ -30,7 +30,7 @@ module RplLang
                                proc do
                                  ticks_since_epoch = Time.utc( 1, 1, 1 ).to_i * 10_000_000
                                  now = Time.now
-                                 @stack << Types.new_object( RplNumeric, now.to_i * 10_000_000 + now.nsec / 100 - ticks_since_epoch )
+                                 @stack << Types.new_object( RplNumeric, (now.to_i * 10_000_000) + (now.nsec / 100) - ticks_since_epoch )
                                end )
       end
     end
diff --git a/lib/rpl/words/trig.rb b/lib/rpl/words/trig.rb
index 7752a01..18681a5 100644
--- a/lib/rpl/words/trig.rb
+++ b/lib/rpl/words/trig.rb
@@ -12,7 +12,7 @@ module RplLang
 
         category = 'Trig on reals and complexes'
 
-        @dictionary.add_word!( ['𝛑', 'pi'],
+        @dictionary.add_word!( %w[𝛑 pi],
                                category,
                                '( … -- 𝛑 ) push 𝛑',
                                proc do
diff --git a/rpl.gemspec b/rpl.gemspec
index 4ed2330..5657f9e 100644
--- a/rpl.gemspec
+++ b/rpl.gemspec
@@ -49,4 +49,5 @@ Gem::Specification.new do |s|
   s.executables << 'rpl'
 
   s.required_ruby_version = '> 2.7'
+  s.metadata['rubygems_mfa_required'] = 'true'
 end
diff --git a/spec/types_spec.rb b/spec/types_spec.rb
index d543d08..01ebbc2 100644
--- a/spec/types_spec.rb
+++ b/spec/types_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
diff --git a/spec/words_branch_spec.rb b/spec/words_branch_spec.rb
index 412af8e..284a190 100644
--- a/spec/words_branch_spec.rb
+++ b/spec/words_branch_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
diff --git a/spec/words_filesystem_spec.rb b/spec/words_filesystem_spec.rb
index 3b62dd7..1ef2ebf 100644
--- a/spec/words_filesystem_spec.rb
+++ b/spec/words_filesystem_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
@@ -17,7 +16,7 @@ class TestLanguageFileSystem < MiniTest::Test
 
     interpreter.run! 'eval vars'
     assert_equal [Types.new_object( RplNumeric, 27 ),
-                  Types.new_object( RplList, [ Types.new_object( RplName, 'trrr' ) ] )],
+                  Types.new_object( RplList, [Types.new_object( RplName, 'trrr' )] )],
                  interpreter.stack
   end
 
@@ -25,7 +24,7 @@ class TestLanguageFileSystem < MiniTest::Test
     interpreter = Rpl.new
     interpreter.run! '"spec/test.rpl" feval vars'
     assert_equal [Types.new_object( RplNumeric, 27 ),
-                  Types.new_object( RplList, [ Types.new_object( RplName, 'trrr' ) ] )],
+                  Types.new_object( RplList, [Types.new_object( RplName, 'trrr' )] )],
                  interpreter.stack
   end
 
diff --git a/spec/words_list_spec.rb b/spec/words_list_spec.rb
index 6a7c0d5..525e7b3 100644
--- a/spec/words_list_spec.rb
+++ b/spec/words_list_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
diff --git a/spec/words_logarithm_spec.rb b/spec/words_logarithm_spec.rb
index bf2d7f1..7de1142 100644
--- a/spec/words_logarithm_spec.rb
+++ b/spec/words_logarithm_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
diff --git a/spec/words_operations-complexes_spec.rb b/spec/words_operations-complexes_spec.rb
index 416ac21..fd36415 100644
--- a/spec/words_operations-complexes_spec.rb
+++ b/spec/words_operations-complexes_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
diff --git a/spec/words_operations-reals-complexes_spec.rb b/spec/words_operations-reals-complexes_spec.rb
index 6c06098..dd86d41 100644
--- a/spec/words_operations-reals-complexes_spec.rb
+++ b/spec/words_operations-reals-complexes_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
diff --git a/spec/words_operations-reals_spec.rb b/spec/words_operations-reals_spec.rb
index 7f27b3e..c93b099 100644
--- a/spec/words_operations-reals_spec.rb
+++ b/spec/words_operations-reals_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
diff --git a/spec/words_stack_spec.rb b/spec/words_stack_spec.rb
index 327be07..a4dfcdd 100644
--- a/spec/words_stack_spec.rb
+++ b/spec/words_stack_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
diff --git a/spec/words_string-list_spec.rb b/spec/words_string-list_spec.rb
index cfd226c..0df3867 100644
--- a/spec/words_string-list_spec.rb
+++ b/spec/words_string-list_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
diff --git a/spec/words_string_spec.rb b/spec/words_string_spec.rb
index 9c7ae82..e223950 100644
--- a/spec/words_string_spec.rb
+++ b/spec/words_string_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
diff --git a/spec/words_test_spec.rb b/spec/words_test_spec.rb
index b75384e..c4ad101 100644
--- a/spec/words_test_spec.rb
+++ b/spec/words_test_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
diff --git a/spec/words_time-date_spec.rb b/spec/words_time-date_spec.rb
index 6a334c1..da8fdfc 100644
--- a/spec/words_time-date_spec.rb
+++ b/spec/words_time-date_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'
diff --git a/spec/words_trig_spec.rb b/spec/words_trig_spec.rb
index 137eaa2..0103926 100644
--- a/spec/words_trig_spec.rb
+++ b/spec/words_trig_spec.rb
@@ -1,4 +1,3 @@
-# coding: utf-8
 # frozen_string_literal: true
 
 require 'minitest/autorun'