Ciro Santilli @cirosantilli 37

This is the part of the formalization of mathematics that deals only with the propositions.

In some systems, e.g. including Metamath, modus ponens alone tends to be enough, everything else can be defined based on it.

A software that implements some database system, e.g. PostgreSQL or MySQL are two (widely extended) SQL implementations.

See: eigenvalues and eigenvectors.