function d3_geo_compose(a, b) {

function compose(x, y) {
  return x = a(x, y), b(x[0], x[1]);
}

if (a.invert && b.invert) compose.invert = function(x, y) {
  return x = b.invert(x, y), x && a.invert(x[0], x[1]);
};

return compose;

}