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Unformatted text preview: roof window. Moving your cursor over an item on
the tool bar turns it into a button. Clicking on the button enters
the symbol or predicate into the proof. The portion of the tool
bar containing predicates can be scrolled back and forth using the
doublearrow buttons on the tool bar. Try this so that you can
see what is available. There are too many predicate and constant
symbols to make them all visible at once. Using Fitch / 33 4.1.4 The proof window The proof window is itself divided into two areas. The larger top
part or “pane” is where you construct proofs. When you add steps
or subproofs to proofs, for example, this is where they will show
up. When you add a step to a proof, the word Rule? appears on
the right. This is a popup menu that you click on to choose the
rule you want to use at the step.
The bottom pane of the proof window is where the problem’s
goals appear, that is, the sentences to be proven. If the goal strip
is not visible, choose Show Goal Strip from the Goal menu. To
hide it, and give yourself more room in the proof pane, choose
Hide Goal Strip from the Goal menu.
At the extreme bottom of the proof window, under the goal
strip, is a Status Line that displays comments and error messages.
The status line is the bottom gray strip where you sometimes see
scroll bars. It is initially blank, but it is used to present a lot of
useful information, especially when proof steps don’t check out.
You can also check the step of the proof in focus by simply clicking
on the status line. 4.2 Creating and editing proofs The body of a proof appears in the large pane in the middle of
the window, sandwiched between the tool bar and the goal strip.
In this section, we explain how to create, modify, and navigate
around a proof. Before doing this, we present a list of some of the
graphical elements you will encounter in the proof pane:
Proof line and Fitch Bar. Proofs and subproofs are
demarcated by a vertical gray line. Attached to the line
is a horizontal bar called the Fitch bar. The Fitch bar
separates the assumptions of the proof from the steps
that follow from those assumptions.
Focus Slider. The focus slider appears just to the left
of the proof and points to the currently focused step. If
there are goals in the goal strip, the focus slider can also
point at one of the goals. There is only one focus slider
in the window at any time. 34 / LPL Software Manual Step Bullet. This circular icon indicates the presence
of a step in the proof. You can either add a new sentence at the step, if none is present, or you can edit an
existing sentence. If step numbers are displayed (Show
Step Numbers from the Proof menu), the step bullet
is replaced by the step number.
Goal Bullet. This “turnstile” icon precedes each of the
goal sentences in the goal strip (unless one is in focus, in
which case the turnstile is replaced by the focus slider).
Constant Box. The constant box appears at the top of
subproofs in which a new constant or constants have been
introduced. The constant box depicted here indicates
that a is a newly introduced constant. The downarrow...
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This document was uploaded on 01/26/2014.
 Winter '14

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