% , True, False , EndOfFile , Infinity , Pi , Undefined .

Constants

% Previous result
True, False Boolean constants
EndOfFile End-of-file marker
Infinity Constant representing mathematical infinity
Pi Mathematical constant, 3.14159...
Undefined Constant signifying an undefined result

% -- Previous result

Internal function
Calling Sequence:
%
Parameters:
Description:
% evaluates to the previous result on the command line. % is a global variable that is bound to the previous result from the command line. Using % will evaluate the previous result (This uses the functionality offered by the LazyGlobal command).

Typical examples are Simplify(%) and PrettyForm(%)to simplify and show the result in a nice form respectively.
Examples: 
In> Taylor(x,0,5)Sin(x)
Out> x-x^3/6+x^5/120;
In> PrettyForm(%)

     3    5 
    x    x  
x - -- + ---
    6    120
See Also:
LazyGlobal .

True, False -- Boolean constants

Internal function
Calling Sequence:
True
False
Description:
True and False are typically the result of boolean expressions like 2 < 3 and True And False.
See Also:
And , Or , Not .

EndOfFile -- End-of-file marker

Internal function
Calling Sequence:
EndOfFile
Description:
End of file marker when reading from file. If a file contains the expression EndOfFile; the operation will stop reading the file at that point.

Infinity -- Constant representing mathematical infinity

Standard math library
Calling Sequence:
Infinity
Description:
Infinity represents infinity. It can be the result of certain calculations.

Note that for most analytic functions Yacas understands Infinity. Thus Infinity*2 will return Infinity, and a < Infinity will evaluate to True.

Examples: 
In> 2*Infinity
Out> Infinity;
In> 2 True;

Pi -- Mathematical constant, 3.14159...

Standard math library
Calling Sequence:
Pi
Description:
Pi represents the value of pi. When the N(..) function is used, Pi is set to the correct value. It is probably better to use Pi than Pi(), for simplification purposes.
Examples: 
In> Sin(3*Pi/2)
Out> -1;
In> Pi
Out> Pi;
In> N(Pi)
Out> 3.1415926535;
See Also:
Sin , Cos .

Undefined -- Constant signifying an undefined result

Standard math library
Calling Sequence:
Undefined
Description:
Undefined is a token that can be returned by a function when it considers its input to be invalid. The resulting output is then undefined.
Examples: 
In> 2*Infinity
Out> Infinity;
In> 0*Infinity
Out> Undefined;
See Also:
Infinity .