What Tim said is right. To add to that, you may also wish to read about
MuSig:
https://blockstream.com/2018/01/23/en-musig-key-aggregation-schnorr-signatures/

Cheers,
Ruben

On Sat, May 15, 2021 at 10:32 PM Tim Ruffing via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> On Sat, 2021-05-15 at 12:21 +0200, vjudeu via bitcoin-dev wrote:
>
>
> >  All that is needed is producing a signature matching the sum of the
> > public keys used in taproot, which is "(a+b-a)*G",
>
> This is simply not true.
>
> Taproot does not enable this, or any other form of "cross-input
> aggregation", i.e., spending multiple UTXOs with a single signature.
>
>
> Tim
>
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