Bivariate normal probability density.
Syntax:		@dbvnorm(x, y, r)
	x:	number
	y:	number
	p:	number, 

 Return:		number
Computes the bivariate normal density with 0 mean, unit variances, and correlation r:
Examples
= @dbvnorm(0, 0, 0.5)
returns 0.18377....
Cross-references