Equivariant

Let us assume that the symmetries defined in Eq. (2) form a closed algebra. It is parametrized by and .

We have the following Cartan form:

(4)

This is always true to the first order in and . For this to be true to all orders in and , we need:

(5)

(6)

Let us summarize the derivation. We have:

Therefore:

(7)

(8)

In passing from (7) to (8) we assumed that both and preserve the measure of integration .

The last line coincides with Eq. (3).