We develop an analogue of universal algebra in which generating symbols are interpreted as relations. prove a variety theorem for these relational algebraic theories, we find that their categories models precisely the definable categories. The syntax our theories is string-diagrammatic, and can be seen extension usual term theories.

It has been a central problem in the theory of quadratic forms to find integers represented by quadratic forms. The celebrated Four Square Theorem by Lagrange [10] was an outstanding result in this study. Ramanujan generalized this theorem and found 54 positive definite quaternary quadratic forms which represent all positive integers [13]. We call a positive definite quadratic form universal, i...

in this paper, we introduce and investigate a subclass of analytic and bi-univalent functions in the open unit disk. upper bounds for the second and third coefficients of functions in this subclass are founded. our results, which are presented in this paper, generalize and improve those in related works of several earlier authors.

We call a positive definite integral quadratic form universal if it represents all positive integers. Then Lagrange’s Four Square Theorem means that the sum of four squares is universal. In 1930, Mordell [M] generalized this notion to a 2-universal quadratic form: a positive definite integral quadratic form that represents all binary positive definite integral quadratic forms, and showed that t...