This web page describes various terms used in these logic web pages.
- aka
- Abbreviation for
also known as
.
- abelian group
- A group for which the binary operation is commutative.
Also called a commutative group.
- bijection
- A function which is both an
injection and a surjection.
Bijections are also called
one-to-one correspondences
.
- canonical
- Meaning
according to a set of rules, or canon
. This word is used
in mathematics to mean that the definition of the object in question
is forced upon us in some way: either because it is the simplest or most
natural such definition that works or more usually because it is the
only such definition.
- embedding
- A map or function taking a structure (such as a group,
ring, field, etc.) into another similar structure , so that
the image of (considered as a
substructure
of )
looks exactly the same as . Such a function will always
be injective and preserve any binary operations
present.
- group
- A set with a binary operation that is associative and has identity
and inverses.
- identification
- When two structures look identical (such as a structure and
the image of it via an embedding) it often makes
sense to regard the two structures as really being the same. We say
that we
identify
them. Such identifications are not strictly
logically correct, because the two copies
of the same object
really are different copies, but the simplification gained
is always worthwhile. Examples include identifying the integers with the
copy of the integers in an ordered field.
- injection
- A function such that for
all from . Injections are also called
one-to-one functions
.
- isomorphism
- A map or function taking a structure (such as a group,
ring, field, etc.) exactly onto another similar structure ,
so that both (considered as a
substructure
of )
and look exactly the same. In other words, an isomorphism
is an embedding that is
surjective as well as injective.
- surjection
- A function such that for all
there is with . Surjections are also called
onto functions
.