Algebra
Algebra (Fr. algèbre) is a branch of mathematics  or logic  concerned with the properties and relationships of abstract entities represented in symbolic form.
Jacques Lacan
Jacques Lacan begins to use algebraic symbols in 1955  in an attempt to formalize psychoanalysis.

The algebraic symbols used by Lacan, which appear principally in the mathemes, schema l and the graph of desire, are listed below, together with their most common meaning.
However, it is important to remember that the symbols do not always refer to the same concept throughout Lacan's work, but are used in different ways as his work develops.

The most important example of such a shift in meaning is the use of the symbol a which is used in radically different ways in the 1950s and in the 1960s.
Even other symbols which are relatively stable in meaning are occasionally used in very different ways.
Therefore some caution should be exercised when referring to the following list of equivalences.