Посилання:C*-algebra generated by four projections with sum equal to 2 / Y. Savchuk // Algebra and Discrete Mathematics. — 2004. — Vol. 3, № 3. — С. 126–134. — Бібліогр.: 8 назв. — англ.
Підтримка:Author expresses his gratitude to Prof. Yuri˘ı S. Samo˘ılenko for the problem stating and permanently attention. I am also indebted to Dr. Daniil
P. Proskurin for his critical remarks and helpful discussions.
We describe the C*-algebra generated by four
orthogonal projections p₁,p₂,p₃,p₄, satisfying the linear relation
p₁ + p₂ + p₃ + p₄ = 2I. The simplest realization by 2 × 2-matrixfunctions over the sphere S² is given.