cannot load such file -- algorithm/diff (LoadError)

<internal:/usr/local/rvm/rubies/ruby-3.0.2/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
<internal:/usr/local/rvm/rubies/ruby-3.0.2/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
/virtual/pink/public_html/wiki/wiki.rb:21:in `<top (required)>'
<internal:/usr/local/rvm/rubies/ruby-3.0.2/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
<internal:/usr/local/rvm/rubies/ruby-3.0.2/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
wiki.rb:15:in `<main>'