The fundamental entity in REDTEN is the ``indexed object'',
which consists of an identifier (a name) and an index enclosed in square
brackets
, for example:
R[a,b,c,d], g[a,1], G[1,2].An index can either be composed of strictly non-negative integers (each of which must lie within the inclusive range for that index-element, see below) and which indicates a specific component of the indexed object, or it can contain identifiers that represent the full range of possible indices, or a combination of both. The contents of the index are described more fully in §2.3 below.
An indexed object is a REDUCE kernel: it is an irreducible
algebraic entity. As such it can be part of any algebraic expression,
although, depending on circumstances, it may or may not be evaluated
to a ``simpler'' form. Before using an index with a name that
name must be made into an indexed object with the mkobj()
command. If an index is
applied to a name that has not been declared as indexed, the system will
prompt for the basic data required to define the object (the
index-type and symmetries, defined below). It is advisable to fully
declare indexed objects before they are used.