Proof.sol

//SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.11;

contract ProofOfExistence1 {
  // state
  bytes32 public proof;
  // calculate and store the proof for a document
  // *transactional function*
  function notarize(string memory document) public {
    proof = proofFor(document);
  }
  // helper function to get a document's sha256
  // *read-only function*
  function proofFor(string memory document) public pure returns (bytes32) {
    return sha256(abi.encode(document));
  }
}