sub fprob { # Upper probability   F(x,n1,n2)
	my ($n, $m, $x) = @_;
	if (($n<=0) || ((abs($n)-(abs(int($n))))!=0)) {
		die "Invalid n: $n\n"; # first degree of freedom
	}
	if (($m<=0) || ((abs($m)-(abs(int($m))))!=0)) {
		die "Invalid m: $m\n"; # second degree of freedom
	} 
	return precision_string(_subfprob($n, $m, $x));
}