approximately
equal,

~ approximately,

0.(12345) the repeating decimal
with the period 12345,

*N * the set of natural
numbers,

*Z* the set of whole
numbers (integers),

*R* the set of real
numbers,

an empty set,

an
infinity sign,

an
element *x * belongs to a set *X*,

*
*
an element *x * doesn't belong to a set *X*,

*X
Y * a set ** X **is a subset
of a set * Y*,

* * a
union of sets *X* and *Y*,

* * an
intersection of sets *X* and *Y*,

*X* \ *Y* a
symmetric difference of sets *X* and *Y*,

{ *u*_{n} } a sequence
with a general term *u*_{n },

[ *a*, *b* ] a numerical
segment,

numerical
semi-segments (semi-intervals),

( *a*, *b *) a numerical
interval,

a
scalar product of vectors * *,

a
vector product of vectors * *,

==> it follows,

<=> equivalent,

perpendicular,

parallel,

a
triangle *ABC,*

a
function and its derivative.