The center of the tree is called the trunk or the root. Each of the other branches is in its own, unique, column which is given a number.

The LogicCoach implementation of trees uses several symbols which are not used in the text. At the bottom of a column which branches, there is a double sided arrow which points to the top items in the left and right decomposition branches. At the bottom of a branch which has not yet been ended, a ? indicates that you have to decide how to continue this branch. The options are to grow it or to close it.

A branch grows by inserting the decomposition of an item in the path from the end of the branch, the ? , to the trunk. A branch is closed by marking its bottom, by replacing the ? , with an X to indicate that you think that it contains a contradiction or by replacing the ? with the word open to indicate that you think that there is no contradiction. Each X and open has to be checked individually. If the mark is correct, then the program will place a √ next to it. If not, an explanation of the difficulty will instead be given.

If there are not enough columns in which to grow the next branch, the program will double the number of columns. When doing so, it renumbers all the columns so that the trunk or root remains in the center. Not every column might used. If there are unused columns, then the visible numbers will not be consecutive.

To change a ? to an X or to open , select the ? and then either press <Del> or right click with the mouse. The action will toggle through the marks. To check the X or the open select it and press <Enter> or double click on it. Ctrl+B is the keyboard shortcut for these actions.

The Mark submenu inside the Options menu presents alternative ways to mark lines and branches.

Note: Once an X or an open have been checked and found correct, they are marked with a √. The √X and the √open cannot be changed.

Click here for a detailed discussion of Exercise T1, Part I, Number 1.