A_BETWEEN()

Calculates the angle formed by 3 points on x,y plane.             
==================================================================
The angle formed by three (3) points on a plane is calculated by  
a_between() by passing the 3 points in x,y coordinate format.  for
example: (all double precision numbers)  x1=10.0, x2=20.0, x3=30.0
y1=20.0, y2=80.0, y3=60.0  angle=a_between(x1,y1,x2,y2,x3,y3)