Complex numbers in 5 dimensions
  A system of commutative complex numbers in 5 dimensions of the form u=x_0+h_1x_1+h_2x_2+h_3x_3+h_4x_4 is described in this paper, the variables x_0, x_1, x_2, x_3, x_4 being real numbers. The operations of addition and multiplication of the 5-complex numbers introduced in this work have a geometric interpretation based on the the modulus d, the amplitude \rho, the polar angle \theta_+, the planar angle \psi_1, and the azimuthal angles \phi_1,\phi_2. The exponential function of a 5-complex number can be expanded in terms of polar 5-dimensional cosexponential functions g_{5k}(y), k=0,1,2,3,4, and the expressions of these functions are obtained from the properties of the exponential function of a 5-complex variable. Exponential and trigonometric forms are obtained for the 5-complex numbers, which depend on the modulus, the amplitude and the angular variables. The 5-complex functions defined by series of powers are analytic, and the partial derivatives of the components of the 5-complex functions are closely related. The integrals of 5-complex functions are independent of path in regions where the functions are regular. The fact that the exponential form of the 5-complex numbers depends on the cyclic variables \phi_1, \phi_2 leads to the concept of pole and residue for integrals on closed paths. The polynomials of 5-complex variables can be written as products of linear or quadratic factors. 
Silviu Olariu (National Institute of Physics and Nuclear Engineering,   Tandem Laboratory, Magurele, Bucharest, Romania)