Determining the structure of market correlation is an important topic in theory and experiments. Under impact Covid-19 pandemic, may be deformed. Therefore, this study examines pandemic’s on structure. This considered VN30 portfolio (including 30 stocks with largest capitalization); collecting period from July 28, 2000, to 30, 2021. The data was divided into 02 phases before after pandemic. Kru...

We prove that a minimal disc in CAT(0) space is local embedding away from finite set of “branch points”. On the way we establish several basic properties surfaces: monotonicity area densities, density bounds, limit theorems and existence tangent maps. As an application, Fáry–Milnor’s theorem setting.