function declareLost(address _lostAddress, bytes32 _nonce) public payable{
        uint256 balance = balanceOf(_lostAddress);
        require(balance > 0);
        require(msg.value >= balance.mul(collateralRate));
        require(claims[_lostAddress].collateral == 0);
        require(validateClaim(_lostAddress, _nonce));

        claims[_lostAddress] = Claim({
            claimant: msg.sender,
            collateral: msg.value,
            timestamp: block.timestamp
        });
        delete preClaims[msg.sender];
        emit ClaimMade(_lostAddress, msg.sender, balance);
    }