def f1(list_of_list):
for x in inner_list:
def f2(list_of_list):
result = []
for inner_list in list_of_list:
if x not in result:
result.append(x)
return result
flat_list = []
for inner_list in list_of_list:
flat_list.extend(inner_list)
return [
x for i, x in enumerate (flat_list)
if flat_list.index (x) == i]
def f3(list_of_list):
result = []
seen = set()
for inner_list in list_of_list:
for x in inner_list:
if x not in seen:
result.append(x)
seen.add(x)
return result

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