Set up maven project
Introduce class Rational
Add basic arithmetic operations to class Rational
Override method toString of Rational
Create test for arithmetic operations, fix bugs in operations
Add negate operation to Rational
fix typos
fix one more typo in test
Express subtraction in terms of addition and negation
Always divide numerator and denominator by gcd
Check denominator not zero
Add test for negative denominator
Add ValueNode and BinaryOperation
Add UnaryOperation node and inverse operation to Rational