## How to Write Formulas in Ghilbert

### Getting Started

• Click the edit button.
• Click the X on the statement on the proof stack to clear the proof:

### Numbers

Single-digit numbers are easy to write in Ghilbert. The number 5 is written as "(5)". But numbers above 10 are difficult to type in the editor. (Click here for an explanation why). There is a button to help you enter formulas numbers in more easily. Above the editor, click on the "Add" button.

A dialog box will appear. Type your favorite number into the dialog box and it will be added into the proof.

### Formulas

In Ghilbert, formulas are written in prefix notation which means that the operator always comes first. For example, (+ A B) is written as "(+ A B)". Every operation has parentheses around it. Let's try writing a simple expression: (+ (+ (* (10) (10)) (+ (* (6) (10)) (5))) (+ (* (4) (10)) (7))).

• First, type a parentheses and an operator "(+ ".
• Click the "num" button, type (+ (* (10) (10)) (+ (* (6) (10)) (5))).
• Click the "num" button, type (+ (* (4) (10)) (7)).
• Add a closed parentheses ")"

The editor should now contain the code (+ (+ (* (10) (10)) (+ (* (6) (10)) (5))) (+ (* (4) (10)) (7))) and the proof stack should contain the expression (+ (+ (* (10) (10)) (+ (* (6) (10)) (5))) (+ (* (4) (10)) (7))).

### Sets

Sets are also tricky to type in the correct format in the editor. To add the set (u. (u. (u. ({} (2)) ({} (3))) ({} (6))) ({} (7))), click the "Add" button and then type: "{2,3,6,7}" in the dialog box.

Similarly to add a tuple like (<,> (<,> (2) (7)) (3)), click the "Add" button and then type: "(2,7,3)" in the dialog box.