function t2( v ) {
		if (
			isnan( v ) ||
			v <= 0.0
		) {
			return NaN;
		}
		return rnorm() / sqrt( rchisq( v ) / v );
	}
Returns a pseudorandom number drawn from a Student's t-distribution with degrees of freedom `v`.

@private
@param {PositiveNumber} v - degrees of freedom
@returns {number} pseudorandom number

@example
var v = t2( 3.0 );
// returns <number>

@example
var v = t2( 0.0 );
// returns NaN

@example
var v = t2( -1.5 );
// returns NaN