This preview shows page 1. Sign up to view the full content.
Unformatted text preview: rmula using that rule. To use this
feature, focus on a step and insert the formula to be derived at this
step. Then select the inference rule to use. Finally select the Add
Support Steps command from Proof menu. If this is disabled,
then the rule does not support this option (or you didn’t choose a
rule or enter a formula.) Otherwise using this command will insert
the necessary steps into the proof. 4.2.13 Starting and ending subproofs A subproof is started by choosing New Subproof from the Proof
menu. When you start a new subproof, you can enter a sentence (or
boxed constant) in the ﬁrst step. Once you are within a subproof,
any new steps you add will be part of that subproof. To add a
step after a subproof, you need to know how to end the subproof.
To end the subproof, focus on any step in the subproof and choose
End Subproof from the Proof menu. This will end the subproof
and give you a new step following that subproof.
If, when you end a subproof, the last step of the subproof is
empty, then that step will just be moved out of the subproof. This
means you can end two embedded subproofs by choosing End
Subproof twice. The ﬁrst time, you will end the innermost subproof and get a new step in the outer subproof. The second time, 40 / LPL Software Manual the new step will be shifted out of that subproof as well. 4.2.14 Boxed constants in subproofs When you start a subproof, a downward-pointing triangle appears
next to the step bullet. This triangle indicates the presence of
a popup menu. If you click down on the triangle, the menu will
appear. In this case, the menu presents you with a list of all the
names available in Fitch. Choosing one of these names adds the
name as a boxed constant—unless it is already boxed, in which
case it is removed from the box. Boxed constants are used in the
rules ∀ Intro, and ∃ Elim. 4.2.15 Collapsing subproofs When you complete a subproof, you might want to “collapse” it so
that you don’t have to think about it any more. This is particularly
true if the subproof is long, and you want to avoid scrolling back
and forth over it while working on a diﬀerent part of the proof.
You can do this using the Collapse Subproof command from
the Proof menu, when you are focused on any step within the
subproof. The subproof will be replaced by a single step containing
an icon to represent the collapsed proof. To open the proof again,
chose Expand Subproof from the Proof menu when you are
focussed on the step containing the collapsed proof. 4.2.16 Deleting subproofs To delete a subproof, focus on the assumption step that begins the
subproof and choose Delete Step from the Proof menu. This
will delete the entire subproof, so make sure you really want to do
that. If you simply want to change the assumption step, edit the
sentence, don’t delete the step. 4.3 Goals The goals for a problem are represented by sentences that appear
in the goal strip at the bottom of the proof window. These are the
sentences that are to be proven in your proof. If the goal strip is
not visible and you would like it to be, choose Show Goal Strip Using Fitch / 41 from the...
View Full Document
This document was uploaded on 01/26/2014.
- Winter '14