Some Basic Sets
Naturals

=  {1,2,3, ... }  natural numbers  
Naturals _{0 }

=  {0,1,2,3, ... }  nonnegative integers  
Integers

=  { ... , 3,2,1,0,1,2,3, ... }  integers  
Integers_{+ }

=  {0,1,2,3, ... }  nonnegative integers, same as Naturals _{0}  
Reals

=  ( ∞, ∞)  real numbers  
Reals_{+}

=  [0, ∞)  nonnegative real numbers  
Complex

=  {x + jy  x ∈ Reals, y ∈ Reals}  complex numbers  
Chars

=  {a, ... , x, A, ... , X, ... }  set of all alphanumeric characters  
Char*

=  {a, ... , x, aa, ab, ... , ax, ... }  set of all finite character strings  
Binary

=  {0, 1}  binary values  
Binary*

=  {0, 1, 00, 01, ... }  set of all finite binary strings 
Sets representing physical quantities
Time

=  (a, b)  a span of time, from a to b. 
Pressure

=  Reals_{+}  air pressure 
Temperature

=  (273.15, &infi;)  temperature (in Centigrade) 
Intensity

=  Reals_{+}  brightness of light 