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<n> <c> <e> // n, c = RSA key len, e = 3 bytes
            | n e c        |
TUCK        | n e c e      | 512   | 1024
1           | n e c e 1    |
AND         | n e c 0/1    | 257   | 513
IF          | n e c        |
DUP         | n e c c      | 512   | 1024
ELSE        | n e c        |
1           | n e c 1      |
ENDIF       | n e c c/1    |

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Title

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const { ECPairFactory } = require('ecpair');
const btc = require('./src');
const ecc = require('tiny-secp256k1');
const { secp256k1, schnorr } = require('@noble/curves/secp256k1');
const psbtutils = require('./src/psbt/psbtutils');
const { reverseBuffer } = require('./src/bufferutils');

const { REVERSE_OPS: rOps } = require('./src/ops');

btc.initEccLib(ecc);

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quine-script = IF TOALTSTACK TOALTSTACK DROP CTV IK CSFS VERIFY FROMALTSTACK DUP 3 SWAP VAULT FROMALTSTACK CLTV ELSE 2DROP CTV ENDIF
state-n-hash { nLockTime(S+n), out(contract, amount(A)+amount(B)) }
settlement-n-hash { nSequence(2w), out(A, amount-n(A)), out(B, amount-n(B)) }

S = 500000000
IK = A+B
Script = CTV IK CSFS VERIFY <quine-script> DUP 3 SWAP VAULT <S+1> CLTV
Tree = Script
Stack = 0 -1 0 <settlement-1-hash> <S+2> <sig> <state-1-hash>

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VAULT quine:

op	stack
START	{1,0,<release_sig>}
<counter>	<counter> {1,0,<release_sig>}
<leaf-update-script-body>	<leaf-update-script-body> <counter> {1,-1,<release_sig>}
TOALTSTACK	<counter> {1,0}
DUP	<counter> <counter> {1,0,<release_sig>}
NOTIF	<counter> <release_sig>

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Abstract

This proposal is an alternative to [bip119][] and [bip118][], providing the functionality of both proposals with minimal additional overhead in many cases, while clearing certain objections to both, and opening clear upgrade paths.

This is, in essence, an initially constrained version of Russel O'Connor's [OP_TXHASH+OP_CSFS proposal][].