is a child of
, each is a parent of the next, until the last, who is a parent of
. But this definition is not adequate unless we add that the number of intermediate terms is to be finite. Take, for example, such a series as the following:—
Here we have first a series of negative fractions with no end, and then a series of positive fractions with no beginning. Shall we say that, in this series,
is an ancestor of