... this text is in progress ...

[ The text shows how first-order predicate logical theories are interpreted very naturally as elements of theory algebras, i.e. schematic relations. The whole approach is based on the subject developed in the Theory algebras of relations. Some month ago I had a version that was almost good enough to be published. This draft (in DVI format) has currently some 256 pages, but it contains many redundancies and is not at all in a decent state. It has some chapters that actually belong to the Theory algebras of relations an it also sketches the construction of finite models for given first-order theories and a more general approach which for a more powerful computable subsystem of theory algebras on relations. The final version of this text will be much shorter. ]