The first problem of algebraic regression.- The first problem of algebraic regression: the bias problem Special Gauss-Markov model with datum defects, LUMBE.- The second problem of algebraic regression Inconsistent system of linear observational equations.- The second problem of probabilistic regression Special Gauss-Markov model without datum defect.- The third problem of algebraic regression.- The third problem of probabilistic regression Special Gauss-Markov model without datum defect.- Overdetermined system of nonlinear equations on curved manifolds inconsistent system of directional observational equations.- The fourth problem of probabilistic regression Special Gauss-Markov model with random effects.- Appendix A-D.- References.- Index.