public Set<String> calculateDependentVariables(final Collection<String> variables) {
        final Set<String> result = new HashSet<>();
        if (variables != null) {
            for (String v : variables) {
                calculateDependentVariablesInternal(result, v);
            }
        }
        return result;
    }
Calculates a set of all variables which are needed (directly or indirectly) to calculate the given vars
main/src/main/java/cgeo/geocaching/utils/formulas/VariableMap.java