  Gottlob Frege ingeniously presented a purely logical definition of the
concept of number. However, one can claim that his definition is, in some way,
circular, as it relies on the concept of one-to-one relation. The concept of
number only makes sense when it presents the property of projection/reflection
or binding. When we consider a number as an abstraction of objects, whatever
they may be, saying that a number that belongs to the concept F is the same as
that which belongs to the concept G means there is a projection/reflection, or
binding, between the objects in F and the objects in G. We present a definition
based on both equivalent approaches. First, we introduce the definition based
on the relations of projection and reflection; then, we present the definition
based on the relation of binding.
