# Trees: Propositional Exercises: Roll your own

Logical System

2013

### Reading

Colin Howson, [1997] Logic with trees Chapter 2

### Exercises

Howson [1997] has a number of exercises. Many of them you will be able to do in the Widget below.

You can also try material of your own.

Here are a few hints

• You have to use the right (unicode/html) logical symbols. Check Writing symbols
• The symbols in use here are ¬ ∧ ∨ → ↔ (so copy and paste or drag and drop these).
• When entering from a selection, the software will take a single formula (say, A) or a comma separated list of formulas (say, A,B,C) or a possibly empty comma separated list of formulas followed by ∴ and another formula (say, A,B,C ∴ D). In the last case it will load the negation of the conclusion.
• Just type, cut and paste, or drag and drop, whatever you wish, into the lower text box. Then make a selection and hit the Start from Selection button.

## Exercise: Roll your own

If you decide to use the web application you can launch it from here Deriver [Howson] — username 'logic' password 'logic'. Then type your material into the Journal. Then select the desired formula(s) and Start Tree off the Actions Menu. [If you find you need to set the Preferences (because you, or someone else, has been doing something totally different with Deriver on the computer in use), set the parser to Howson. The title bar of the Deriver window will show you what system you are running e.g. 'DeriverDefault', 'DeriverGentzen', etc.]