/**
* Small-step semantics
*
* @return The expression after taking a single reduction step
*/
public Aexp reduce(Memory memory) {
if (!a1.isValue()) return new Sub(a1.reduce(memory), a2);
else if (!a2.isValue()) return new Sub(a1, a2.reduce(memory));
else return new ConstantInt(a1.value() - a2.value());
}
