/**
   Computes the square root of a real number.
   @param x a number (>= 0)
   @raturn the square root of x.
*/
double sqrt(double x)

/**
   Determines the midpoint between two points.
   @param a a Point
   @param b another Point
   @return the point that is midway between points a and b.
*/
Point midpoint(Point a, Point b)

/**
   Computes the area of a circle
   @param c a circle 
   @return the area of the circle.
*/
double area(Circle c)

/**
   Determines the Roman number equivalent of a number.
   @param n an integer (between 1 and 3999)
   @return the string representation of a Roman number.
*/
string roman_numeral(int n)

/**
   Computes the slope of a line segmet.
   @param a a line (must not be vertical)
   @return the slope of the line segment.
*/
double slope(Line a)

/**
   Determines if a given year is a leap year.
   @param y a year
   @return true if y is a leap year; false otherwise.
*/
bool is_leap_year(year y)

/**
   Returns the name of a weekday.
   @param w 0 = Monday, 1 = Tuesday ... 6 = Sunday
   @return the string name of the weekday denoted by w.
*/
string weekday(int w)