private boolean solvePlusInGroup(int l, int r)
                                        throws ContradictionException {
        boolean tableModified = false;
        int pluses = 0;
        for (int i = l; i < r; ++i) {
            if (table[i][ENV_COL] == Resolution.Plus) {
                ++pluses;
            }
        }
        if (pluses == 1) {
            for (int i = l; i < r; ++i) {
                if (table[i][ENV_COL] != Resolution.Plus) {
                    boolean setMinusValue = setMinus(i, ENV_COL);
                    tableModified = tableModified || setMinusValue;
                }
            }
        }
        return tableModified;
    }