How does point comparison work for the identity / point at infinity?

[matthiasgeihs]

Point equality is implemented as:

elliptic/lib/elliptic/curve/mont.js

Lines 163 to 165 in 43ac7f2

	Point.prototype.eq = function eq(other) {
	return this.getX().cmp(other.getX()) === 0;
	};

The identity (aka point at infinity) is any point that has 0 in its z-coordinate:

elliptic/lib/elliptic/curve/mont.js

Lines 77 to 80 in 43ac7f2

	Point.prototype.isInfinity = function isInfinity() {
	// XXX This code assumes that zero is always zero in red
	return this.z.cmpn(0) === 0;
	};

How would point comparison give the correct result when comparing against the point at infinity?