On the diamenter of Lascar strong types (after Ludomir Newelski)

This is an exposition a theorem of mathematical logic which only assumes the notions of structure, elementary equivalence, and compactness (saturation). Newelski proved that type-definable Lascar strong types have finite diameter. Our exposition is based on a proof that appears in Pelaez’ thesis - up to a minor difference: the notion of weak c-free is replaced with the notion of non-drifting that is introduced here.