<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def combine_sig( global_R: Ed25519PublicPoint, sigs: Iterable[Ed25519Signature] ) -> Ed25519Signature: """Combine a list of signatures into a single CoSi signature."""

    S = [_ed25519.decodeint(si) for si in sigs]
    s = sum(S) % _ed25519.l
    sig = global_R + _ed25519.encodeint(s)
    return Ed25519Signature(sig)