Function and Overloaded Operator Parameters

Alright I am reading Practical C++ and this is what I am confused about.

struct Point2d

{

float x;

float y;

};

Point2d operator-(const Point2d& p1, const Point2d& p2);

Point2d Subtract(const Point2d& p1, const Point2d& p2);

Point2d operator-(const Point2d& p1, const Point2d& p2)

{

Point2d pt;

pt.x = p1.x - p2.x;

pt.y = p1.y - p2.y;

return pt;

}

Point2d Subtract(const Point2d& p1, const Point2d& p2)

{

Point2d pt;

pt.x = p1.x - p2.x;

pt.y = p1.y - p2.y;

return pt;

}

later on it goes to

Point2d pt1 = {10.0f, 16.0f};

Point2d pt2 = {8.0f, 7.0f};

Point2d pt3 = Sbutract(pt1, pt2);

pt3 = pt1 - pt2;

what I am wondering don't you have to pass the parameters in with the same name shouldn't pt1 and pt2 be p1 and p2??