	require(preimagePartOk[_key][_offset], "pre-image must exist");
	// revert if part offset >= size+8 (i.e. parts must be within bounds)
	if iszero(lt(_partOffset, add(size, 8))) {
		// Store "PartOffsetOOB()"
		mstore(0x00, 0xfe254987)
		// Revert with "PartOffsetOOB()"
		revert(0x1c, 0x04)
	}
