2.5 Conjuntos abiertos

New channel César Alberto Aguillón Barrera: title sample judged 'whole' (This is a full set of long-form university-level math lecture recordings (real analysis, topology, differential topology); passed a second screen for sellers/exam-prep/re-uploads; 3 of 3 sampled transcripts showed teaching, 0 not; every title checked strictly; oEmbed verified.