Halliday & Matthiessen (2014: 644):
The most direct form of lexical cohesion is the repetition of a lexical item; e.g. bear in
Algy met a bear. The bear was bulgy
Here the second occurrence of bear harks back to the first. In this instance, there is also the reference item the, signalling that the listener knows which bear is intended; and since there is nothing else to satisfy the the, we conclude that it is the same bear. But this referential link is not necessary to lexical cohesion; if we had Algy met a bear. Bears are bulgy, where bears means ‘all bears’, there would still be lexical cohesion of bears with bear. In this case, however, there would be only one tie; whereas in the example cited first there are two, one referential (the) and one lexical (bear).