Long sentence

[Cooliegirly]

What is this sentence trying to say:

This is exactly what he argued that the ancient Greek philosopher Aristotle had done by focusing not on the similarities in the motion of objects but on the differences that are attributable to the effect of a medium.

Should it be:

This is exactly what he argued that the ancient Greek philosopher Aristotle had done by focusing not on the similarities in the motion of objects but on the differences that are attributable to the effect of a medium.

Or:

This is exactly what he argued that the ancient Greek philosopher Aristotle had done by focusing not on the similarities in the motion of objects but on the differences that are attributable to the effect of a medium.

[Mister Micawber]

.
If I understand your emboldening code properly, it is the second case:

He argued that Aristotle had done it by focussing on the differences.
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Native English teacher at Mister Micawber's