Product p = new Product( (Variable)this, false );
Product q = new Product( (Variable)x, false );
return p.multiply( q );
} else if( x instanceof Sum ){
Product p = new Product( (Variable)this, false );
return p.multiply( (Expression)this );
} else if( x instanceof Product ){
Product p = new Product( (Variable)this, false );
return p.multiply( (Product)x );
} else if( x instanceof Expression ){
Product p = new Product( (Variable)this, false );