Table 1.

Some examples of virus spread terms.

G(x, y)	Hx(y)	Hy(x)	Fast or slow?
x/(x +y + ε)	y	x	Fast
$$\frac{x}{\sqrt{x+y+{\mathit{\epsilon }}_1}\left(\sqrt{x}+\sqrt{y}+\sqrt{{\mathit{\epsilon }}_2}\right)}$$	y	x	Fast
$$\frac{x}{\left(x+{\mathit{\epsilon }}_1\right)\left(y+{\mathit{\epsilon }}_2\right)}$$	const	const	Slow
$$\frac{x}{\left(\sqrt{xy}+{\mathit{\epsilon }}_1\right)\left(\sqrt{x}+\sqrt{y}+\sqrt{{\mathit{\epsilon }}_2}\right)}$$	$\sqrt{y}$	$\sqrt{x}$	Slow
$$\frac{x}{\sqrt{x}\left(y+c\right)+x+\mathit{\epsilon }}$$	y	$\sqrt{x}$	Slow