The receive() function must be called upon transfers

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Calling the tranfer() function should trigger a call to the receive() function of the recipient, whenever this function exists:

https://docs.soliditylang.org/en/latest/contracts.html#receive-ether-function

For example, consider the contracts:

contract C { 
      uint x; 
      receive() external payable { x = 5; }
}
contract D { 
      constructor() payable { } 
      function f(address a) public { payable(a).transfer(1); }
}

After a call to f("0xC"), the value of state variable x in contract C should be equal to 5.