Research Article

Greedy Expansions with Prescribed Coefficients in Hilbert Spaces

Figure 1

An illustration for certain steps of the proof of Theorem 3. All vectors except lie in the vertical plane; (as well as ) lies in the horizontal plane; represents any vector from the set . The spherical law of cosines is applied to angles formed by the vectors , , . The law of sines is applied to the triangle formed by vectors , , .