(ref.doc)background

Basic concepts:

p vii
To specify, design, implement, read, understand, document, appreciate,
criticize, test, qualify, debug, maintain, adapt, port or improve
programs, we need to master the notations which serve to express their
final forms: programming languages.

p 6
Terminology note: instruction, statement
In the discussion of axiomatic semantics, assertions may be described
as *statements* (in the ordinary sense of the term) about
*instructions*.

p 7-8 
At the root of differences between mathematical notations and
programs, you will find an important notion: referential transparency.
[...] Programming languages [...] violate referential transparency if
they permit side effects. [...] Aliasing may also cause violations of
referential transparency.

p 12
[Programming languages are] elaborate notations for thinking and
problem-solving.


Mathematical background:

p 19, 2.3.2 Defining sets
Extension, comprehension.
(Note: a class is a set plus a scope).