To enter the same thing from the keyboard would

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Unformatted text preview: using the Undo and Redo commands from the File menu. 3.3.1 Writing formulas Tarski’s World makes writing first-order formulas quite painless. As you may have noticed while playing with the sentence toolbar, when you enter a predicate, like Tet or BackOf, the insertion point locates itself in the appropriate position for entering “arguments”—variables (u, v, w, x, y, z) or individual constants (a, b, c, d, e, f). What this means is that a sentence like BackOf(a,b) can be entered into the sentence list with three mouse clicks in the toolbar: first on the BackOf button, then on the a button, then on the b button. To enter the same thing from the keyboard would require 11 keystrokes. In order to allow you to write more readable formulas, Tarski’s World treats brackets (“[ ]”) and braces (“{ }”) as alternatives to parentheses when grouping formulae. Thus, for example, you could 22 / LPL Software Manual write [LeftOf (a, b) ∧ Large(a)] and Tarski’s World will read this sentence as (LeftOf (a, b) ∧ Large(a)). But you have to type brackets and braces from the keyboard, and you must use parentheses to indicate the arguments in atomic sentences. 3.3.2 Commenting your sentences You can add comments to your sentences in a way that will be ignored by the program when it is checking to see if they are well formed or true. You do this by prefacing each line of text you want ignored by a semicolon (;). This will cause Tarski’s World to ignore anything that follows on the same line. Tarski’s World displays all of the characters in the comment in green to remind of their (in)significance. 3.3.3 Creating a list of sentences To create a whole list of sentences, you first enter one sentence, and then choose Add Sentence After from the Sentence menu. You are given a new, numbered line, and can then enter a new sentence. If you hit the Return (or Enter) key, this will not start a new sentence, but will simply break your existing sentence into two lines. Use Add Sentence After! Instead of choosing Add Sentence After from the Sentence menu, you can do this from the toolbar by clicking the Add After button or you can do it directly from the keyboard in two ways. You can type Shift-Return (that is, hit the Return (or Enter) key while holding the shift key down) or use the keyboard equivalent shown in the menu. To insert a new sentence in your list before the current sentence, choose Add Sentence Before from the Sentence menu, or using the Add Before button on the toolbar. 3.3.4 Moving from sentence to sentence You will often need to move from sentence to sentence within a list of sentences. You can move the insertion point with the up and down arrow keys (↑, ↓) on the keyboard or by clicking on the sentence of interest with the mouse. The left and right arrow keys (←, →) on the keyboard also move the insertion point, but only Using Tarski’s World / 23 Table 3.1: Keyboard equivalents for typing symbols. Symbol Key Symbol Key ¬ ∧ → ∀ ⊆ ∼ & $ @ = ∨ ↔ ∃ ∈ # | % / \ within a s...
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This document was uploaded on 01/26/2014.

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