The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
46. And on account of the transfer (of particulars).
That those agnis enter into the sacrificial action follows
moreover from the fact that the text extends to them (the injunctions given about the agni made of bricks). Compare the passage, 'Thirty-six thousand shining Agnis; each one of them is as large as the previously mentioned Agni.' Such extension of injunctions is possible only where there is general equality. The text therefore by extending the determinations relative to the previous agni, i.e. the agni built of bricks, which forms a constituent element of the sacrificial action, to the fanciful agnis, intimates thereby that they also form part of the sacrificial performance.