```
#!/usr/bin/env python3

ifield = 0

sudoku = []

f = open('input.txt', 'r')
while ifield < 36:
# skip "Field"
f.readline().strip()

field = []
for i in range(6):
line = f.readline().strip().split(' ')
field.append(line)
sudoku.append(field)

# skip empty line
f.readline().strip()

ifield += 1

f.close()

def print_characters():
for ifield in range(36):
for y in range(6):
for x in range(6):
print(sudoku[ifield][y][x])

# print_characters()
# ./solution.py | sort | uniq
abc = set([c for c in '_{}0123456abcdefghijklmnopqrstuvwxyz'])

def print_sudoku():
for ifield in range(36):
print('Field', ifield)
for y in range(6):
for x in range(6):
print(sudoku[ifield][y][x], end='')
print()
print()

stars_are_there = True
while stars_are_there:
stars_are_there = False
for ifield in range(36):
for y in range(6):
for x in range(6):
if sudoku[ifield][y][x] == '*':
stars_are_there = True

# look for possible variants within the same field
written = set()
for yy in range(6):
for xx in range(6):
v = sudoku[ifield][yy][xx]
if v != '*':
written.add(v)
available_in_field = abc - written

# look for possible variants within the same column
written = set()
for iifield in range(36):
v = sudoku[iifield][y][x]
if v != '*':
written.add(v)
available_in_column = abc - written

# print(ifield, y, x, available_in_field, available_in_column)
available = available_in_column.intersection(available_in_field)
# print(ifield, y, x, available)
if len(available) == 1:
sudoku[ifield][y][x] = available.pop()

print_sudoku()
```