Possible fresh variable name collisions

[cameel]

Currently Prolog.rewriteVariable() works with the assumption that hashing a variable name together with an integer won't ever produce a collision with an existing variable:

SolPrologV2/src/Prolog.sol

Lines 77 to 82 in 47bb8ec

	function rewriteVariable(uint _symbol, uint _uniqueContext) private pure returns (uint) {
	bytes32[] memory input = new bytes32[](2);
	input[0] = bytes32(_symbol);
	input[1] = bytes32(_uniqueContext);
	return uint(keccak256(abi.encodePacked(input)));
	}

A collision unlikely but not impossible. We may want to use a safer method of obtaining fresh variable names.