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Unformatted text preview: is faster using the tool bar. However some sentences must be entered using the keyboard, since
the predicates, names, or sentence letters may not appear on the
tool bar. For example, you will have to type parts of the sentence
P → (Q ∨ R), since P, Q, and R don’t appear on the tool bar. 36 / LPL Software Manual Figure 4.2: Using hierarchical menus to specify rules. 4.2.6 Deleting steps To delete a step, focus on the step and choose Delete Step from
the Proof menu. If you delete the assumption step of a subproof
(the step just above the Fitch bar), the entire subproof containing
that step will be deleted. Be careful in deleting assumption steps,
since you could lose a lot of work. If you simply want to change
the assumption, just edit the sentence.
You can either cut or delete a range of steps by using the selection rectangle on the tool bar. Use the rectangle tool to select
the steps you want and then cut or delete them. 4.2.7 Specifying a step’s rule When you add a new step, the word “Rule?” appears to the right
of the step. To specify a rule for the step, click down on the word
“Rule?” A popup menu will appear. This menu has ﬁve submenus
plus the rule of Reit.
The submenus are attached to Intro, Elim, Con, Lemma,
and Induction. Moving the cursor over these submenus will cause
a second menu to appear with a list of further options. To specify
the rule of, say, Negation Introduction, ﬁrst move the cursor over
the item Intro. Then, when the second menu appears, move the
cursor to the item ¬ (or “not”) and release the mouse button. This
operation is illustrated in Figure 4.2. Similarly, to specify the rule
of Taut Con, ﬁrst move the cursor over the item Con and then
choose Taut from the second menu.
You can also specify a rule from the keyboard, by typing the Using Fitch / 37 Table 4.1: Keystroke equivalents for specifying rules.
Rule Equiv Rule Equiv ∧ Elim
↔ Elim Opt(Alt)-&
Opt(Alt)-% ∧ Intro
↔ Intro Shift-Opt(Alt)-&
Shift-Opt(Alt)-% = Elim
∃ Elim Opt(Alt)-=
Opt(Alt)-/ = Intro
∃ Intro Shift-Opt(Alt)-=
Taut Con Opt(Alt)-R
Opt(Alt)-T FO Con
Ana Con Opt(Alt)-F
Opt(Alt)-A appropriate keystroke equivalent. A list of these appears in Table 4.1. Note that in using these keyboard equivalents, you should
not hold down the shift key unless it is explicitly mentioned in the
table. For example, to specify the rule ∀ Elim, you will actually
type Option-2 (Macintosh) or Alt-2 (Windows); holding down the
shift key will change the rule to ∀ Intro instead. In most cases, we
have listed the shifted (“uppercase”) characters because they are
easier to remember. For example, it is easier to remember that ∧
Elim is Option-& than to think of it as Option-7. 4.2.8 Changin...
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- Winter '14