/usr/share/ri/1.8/system/Mutex/ is in ri1.8 1.8.7.352-2ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/ri/1.8/system/Mutex/cdesc-Mutex.yaml
/usr/share/ri/1.8/system/Mutex/exclusive_unlock-i.yaml
/usr/share/ri/1.8/system/Mutex/lock-i.yaml
/usr/share/ri/1.8/system/Mutex/locked%3f-i.yaml
/usr/share/ri/1.8/system/Mutex/new-c.yaml
/usr/share/ri/1.8/system/Mutex/synchronize-i.yaml
/usr/share/ri/1.8/system/Mutex/try_lock-i.yaml
/usr/share/ri/1.8/system/Mutex/unlock-i.yaml
/usr/share/ri/1.8/system/Mutex_m/append_features-c.yaml
/usr/share/ri/1.8/system/Mutex_m/cdesc-Mutex_m.yaml
/usr/share/ri/1.8/system/Mutex_m/define_aliases-c.yaml
/usr/share/ri/1.8/system/Mutex_m/extend_object-c.yaml
/usr/share/ri/1.8/system/Mutex_m/mu_extended-i.yaml
/usr/share/ri/1.8/system/Mutex_m/mu_initialize-i.yaml
/usr/share/ri/1.8/system/Mutex_m/mu_lock-i.yaml
/usr/share/ri/1.8/system/Mutex_m/mu_locked%3f-i.yaml
/usr/share/ri/1.8/system/Mutex_m/mu_synchronize-i.yaml
/usr/share/ri/1.8/system/Mutex_m/mu_try_lock-i.yaml
/usr/share/ri/1.8/system/Mutex_m/mu_unlock-i.yaml
/usr/share/ri/1.8/system/Mutex_m/new-c.yaml