Bivariate normal cumulative probability.
Syntax:		@cbvnorm(x, y, r)
	x:	number
	y:	number
	p:	number, 

 Return:		number
Computes the cumulative distribution function for a bivariate normal with 0 mean, unit variances, and correlation r:
where 
Examples
= @cbvnorm(0, 0, 0.5)
returns 0.33333....
Cross-references