Values of formulas:

T the formula is true in the world
F the formula is false in the world
U the formula contains free variables that are undefined in the world
? the formula contains a syntax error

Saving files:

For security reasons, the operations "Save as" and "Open" are not permitted for a Java Applet. In order to save and load worlds and formulas you have to download the Java archive tarski.jar and then start the application on your computer by double clicking the icon or using one of the following commands:
java -jar tarski.jar
java -classpath tarski.jar ch.ethz.inf.rs.Tarski