/usr/share/doc/ruby-treetop/examples/ is in ruby-treetop 1.4.10-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/doc/ruby-treetop/examples/lambda_calculus/
/usr/share/doc/ruby-treetop/examples/lambda_calculus/arithmetic.rb
/usr/share/doc/ruby-treetop/examples/lambda_calculus/arithmetic.treetop
/usr/share/doc/ruby-treetop/examples/lambda_calculus/arithmetic_node_classes.rb
/usr/share/doc/ruby-treetop/examples/lambda_calculus/arithmetic_test.rb
/usr/share/doc/ruby-treetop/examples/lambda_calculus/lambda_calculus
/usr/share/doc/ruby-treetop/examples/lambda_calculus/lambda_calculus.rb
/usr/share/doc/ruby-treetop/examples/lambda_calculus/lambda_calculus.treetop
/usr/share/doc/ruby-treetop/examples/lambda_calculus/lambda_calculus_node_classes.rb
/usr/share/doc/ruby-treetop/examples/lambda_calculus/lambda_calculus_test.rb
/usr/share/doc/ruby-treetop/examples/lambda_calculus/test_helper.rb