(6:6) "All the days of his Naziritism to the L-rd, (upon the soul of a dead one he shall not come."): to equate the days after his Naziritism with the days in the midst of his Naziritism until he brings the offering. (i.e., If he undertook a thirty-day Naziritism and completed it but had not yet brought an offering, he may not become tamei for the dead until he does so.) Or, perhaps he is liable for tumah only until he completes his period of Naziritism, (even if he has not yet brought the offering.)
You reason (as follows): Since a Nazirite is forbidden to drink wine and to become tamei, then if I have learned re wine that the days after his Naziritism are equated with the days in the midst of his Naziritism until he brings the offering, so, re tumah. And, furthermore, it follows a fortiori, viz.: If with wine, which does not void (the count), the days after the Naziritism are equated with the days in the midst of the Naziritism until he brings the offering, how much more so (should this obtain) with tumah, which does void the count! — No, this may be so with wine, where no act in its category (the drinking of wine) is permitted (to a Nazirite,) wherefore the days after the Naziritism are equated with the days in the midst of the Naziritism — as opposed to tumah, where an act in its category (i.e., meth-mitzvah) is permitted — wherefore the days after the Naziritism are not to be equated with the days in the midst of the Naziritism before the bringing of the offering.
This is refuted by shaving (i.e., the shaving of a Nazirite leper on the seventh day), where an act in its category (the category of shaving) is permitted, in spite of which the days after the Naziritism are equated with the days in the midst of the Naziritism before the bringing of the offering. And, furthermore, it follows a fortiori, viz.: If with shaving, which does not void the whole (count), the days after the Naziritism are equated with the days in the midst of the Naziritism before the bringing of the offering, then with tumah, which does void the whole, how much more so! — No, this may be so with shaving, where the shaver was equated (for liability) with the shaved one (i.e., the Nazirite who shaves himself) — wherefore this equation was made, as opposed to tumah, where the defiler was not equated (for liability) with the defiled (i.e., the Nazirite who defiles himself) — wherefore the days after the Naziritism are not to be equated with the days before the Naziritism before the bringing of the offering. — This is refuted by (the instance of) wine, where one who causes the Nazirite to drink was not equated (for liability) with the drinker (i.e., the Nazirite himself), in spite of which the equation was made.
And this would indicate re tumah, that even though the defiler is not equated with the defiled, the days after the Naziritism are to be equated with the days in the midst of the Naziritism before the bringing of the offering. —- And the argument goes round and round. It is, therefore, written (6:20) "… and then (after the offering) the Nazirite may drink wine." Now may a Nazirite drink wine? Rather, the verse is "extra" to the end of formulating an identity (gezeirah shavah), viz.: It is written here (12) (in respect to tumah) "Nazirite," and there (20) (in respect to wine) "Nazirite."
Just as there, the days after the Naziritism are equated with the days in the midst of the Naziritism before the bringing of the offering, so, there, (in respect to tumah).