Hi anon, I'm just a learner, but here are my two cents. I don't normally see a colon after "it has been ascertained that". Perhaps this helps: Colons are a lot less attractive for several reasons: firstly, they give you the feeling of being rather ordered around, or at least having your nose pointed in a direction you might not be inclined to take if left to yourself, and, secondly, you suspect you’re in for one of those sentences that will be labeling the points to be made: firstly, secondly and so forth, with the implication that you haven’t sense enough to keep track of a sequence of notions without having them numbered.
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Colons are a lot less attractive for several reasons: firstly, they give you the feeling of being rather ordered around, or at least having your nose pointed in a direction you might not be inclined to take if