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A moduli spase consists in classifying geometric objects up tp equivalence relations and its point are in 1-1 corrospondence with equivalence classes. One of the most important moduli spaces in algebraic geometry is «moduli space of stable n-pointed curves of genus zero» which has many applications in mathematics and theoretical physics.In [10] Knudsen shows that for every n 3 there is a smooth projective variety Xn that is a moduli space for stable n-pointed curves of genus zero.In this thesis we study moduli spaces and introduce Xn and its relation with cross ratios. This way we show Xn is smooth projective variety and a fine moduli space. [5] After that we study a paper by Sean Keel. [9]... 

One of the most important philosophical issues in biology that continues to receive attention is the issue of species. Since ancient times, the classification of living organisms and the definition of species as its foundation have been of great importance to thinkers and knowledge seekers. In this research, while addressing various perspectives, this subject is still being examined today. This research has been divided into two main sections. The first section includes the definition of the problem and various perspectives on it. The main perspective focuses on the influence of genetics in strengthening or weakening it, while the secondary perspective, although interesting, is seen as a...