public boolean isEmptyAndNotNeeded(final String var) {
        final VariableState state = get(var);
        return state == null || (StringUtils.isBlank(state.getFormulaString()) && state.isNeededBy.isEmpty());
    }
Returns true if (and only if) given var is either NOT present in the map OR
has an empty formula and is not needed by any other var
main/src/main/java/cgeo/geocaching/utils/formulas/VariableMap.java