[see also: notice, observe, see, remark
Note that (3) is merely an abbreviation for the statement that......
Perhaps it is appropriate at this point to note that a representing measure is countably additive if and only if......
Part (b) follows from (a) on noting that A=B under the conditions stated.
Before going to the proof, it is worth noting that......
......, as noted <as was noted> in Section 2. [Not: “as it was noted”]
It should be noted that......