def equivalenceClasses(input, output):
"""
(File, File) -> None
Computes equivalence classes using a partition.
First reads an integer from the input stream that
specifies the size of the universal set.
Then reads pairs of integers from the input stream
that denote equivalent items in the universal set.
Prints the partition on end-of-file.
"""
line = input.readline()
p = PartitionAsForest(int(line))
for line in input.readlines():
words = line.split()
i = int(words[0])
j = int(words[1])
s = p.find(i)
t = p.find(j)
if s is not t:
p.join(s, t)
else:
output.write("redundant pair: %d, %d\n" % (i, j))
output.write(str(p) + "\n")
