# Mathematical Background and Algorithms of a Collection of Android Apps for a Google Play Store Page
## 1 Introduction
### Private File Manager App  
We will present the mathematical background and algorithm for a private file manager app. In the current world, smartphones and tablets have entered at light speed; nowadays, hardly anyone in cities has not owned at least one smartphone or tablet [11]. Smartphones or tablets can also be very intimate, storing a lot of sensitive user information [12]. Having access to someone's smartphone or tablet is almost like having access to that person's digital life [13]. Smartphones and tablets can store many accounts, passwords, and almost any information that can be hacked if the person is the target of a cyber attack [14]. If someone installs an app, it will allow the creator of the app to have access to a lot of sensitive user information, that is, the app can access a very intimate part of the user's digital life [15]. As time passes, many new applications appear, each of them wanting access to many intimate data [16]. Today, data privacy is very important; there have many scandals of private information being released, a lot of privacy consent is given, and GDPR declaration forms have to be accepted [17]. As time passes, privacy will become more important and much effort will be made to protect privacy [18]. After each version of the Android operating system is released, the developers analyze privacy issues and perform software updates to increase privacy [19]. In other words, each version is more and more secure [20]. To come in handy for this privacy issue, this article presents the creation of an app that increases privacy in a way that was not thought of when creating updates to the Android operating system until now (Android 12L (API 32) (Google, Mountain View, CA, USA)). The app uses the functionality of Linux (because Android is a Linux-based operating system), where files beginning with a dot (\".\") are hidden. The app renames the files to begin with a dot (\".\"). To unhide them or reverse the process, the dot (\".\") is removed from  
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the beginning of the filename. The app can be used to hide images or videos from the Gallery app on the Android phone or tablet. The app can also hide other files, but images or videos are perhaps some of the most sensitive data for the average user of a smartphone or tablet. The app can be accessed with a password, so only the owner of the smartphone or tablet can hide images or videos from the Gallery app on the Android smartphone or tablet. After the images and videos are hidden in the private file manager app, anyone who accesses the Gallery app of the Android smartphone or tablet will be able to view only the files the user allows anyone to view, and the files the user had posted or would post to social media sites. The app is special because it is not very easy to create an app that shows all hidden files, and on Android, the standard file manager cannot really hide all files, especially not images or video files. The method of hiding files is carried out with external apps with the \".nomedia\" file in a folder, but this will hide an entire folder, not each folder/file selected individually by the user. Also, file hiding can be problematic in an Android system because sometimes the file system needs to be refreshed or the operating system needs to be rebooted. Sometimes, the file is renamed to begin with a dot (\".\"), but is still visible; in this situation, a phone reboot is needed. Because the app deals with sensitive data, such as images and videos, the app must be robust to prevent the user from losing any of their files. There is also the issue that not all file managers let the user rename a file to begin with a dot (\".\") to hide it. Simply, doing this will not rename the file; it will allow one to rename the file to anything else, but not begin with a dot (\".\"). A command must be found that will rename a file to begin with a dot (\".\"). Ontology-driven strategies have been suggested to improve file management by supporting semantic structure and retrieval. [PERSON] et al.