The cells H1, H3, H4, G6 and H7 can together accept various combinations of values. But some combinations of values can be excluded, because they would leave some cells with no potential values.
More precisely, the following combinations of values are not possible
for the cells H1, H3, H4, G6 and H7:
1, 0, 0, 0 and 1 because the value can occur only once in the region
1, 0, 1, 0 and 0 because the value can occur only once in the region
1, 1, 0, 0 and 0 because the value can occur only once in the region
1, 7, 2, 5 and 4 because the cell H6 must contain 2, 4 or 5
Because some potential values of H1 occur in none of the remaining combinations, they can safely be removed.