#### Definition: Cartesian multiplicationEdit

*Cartesian multiplication* of two sets A, B with |a>,|b> elements is defined as

#### Definition: ProjectionEdit

*Projection* f from set A to set B is AxB subset defined as

and notation is used.

#### Definition: Body of numbersEdit

*Body of numbers* T is defined as

#### Definition: Vector spaceEdit

*Vector space* V is defined as

#### Definition: FunctionEdit

*Function* is a projection , which meets

#### Definition: FunctionalEdit

*Functional* is a projection , which meets

#### Definition: OperatorEdit

*Operator* is a projection , which meets