42   return new Sum(*
this);
 
Sum & operator=(const Sum &rhs)
 
TE_DEFINE_VISITABLE Sum(Expression *arg)
Constructor. 
 
Expression * clone() const 
It creates a new copy of this expression. 
 
A base class for unary functions. 
 
UnaryFunction & operator=(const UnaryFunction &rhs)
 
This is an abstract class that models a query expression.