7

direct employment of the complicating operations.

I have thus sketched this line of thought in order
to give you a rough notion of the kind of reasoning
needed in this business. The reasoning which determined
the first part of the rule is altogether too complicated to be
explained orally. It would be easy enough to de-
scribe a way of getting rid of all the lines of
identity in a graph while preserving its entire
meaning. But the difficulty would be that in
the case of a not excessively complicated graph, the different
spots would run up into the thousands. But an
overwhelming majority of them would be entirely
useless. What is wanted is to join the
junctures of corresponding [marks?] of all the different replicas of the same
spot which occurs both within an odd