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# Lab Overview

A J Lab file combines a text description and executable J code in a single file. The Lab system lets you step through the file, displaying the text and executing the code. The user is in a normal J session, and can try out other J expressions while running the lab.

A Lab is structured into one or more chapters, each containing one or more sections. The user can go through chapters in any order, but the sections within each chapter must be run sequentially.

Lab files are either ordinary text files with extension `.ijt`; or rich-text files with extension `.rtf`. Rich-text files permit greater control over text formatting, but work only in Windows 95/NT, and take more effort to set up.

You can create the ijt files using Lab Author or any text editor such as Notepad; and create the rtf files with word processors such as Word or WordPad, see Rich-Text.

Lab files provided with J are stored under the subdirectory system\extras\labs. The directory system\extras\labs\personal is available for the user, though you can create labs in any directory - if so, you should update file system\extras\labs\labdir.ijs.

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