SPECIAL SYMBOLS IN ISETL

**        Exponentiation. Example: 2**3 = 8

:=         Assignment. Used to define values for variables. These variables can represent any mathematical object: a number, a Boolean, a set, a tuple, a string, a function. Example: f := func(x); etc.

/=         Inequality. This means "not equal to".

#          This can be either cardinality of a set or length of a tuple. Example: #{1,3,1}= 2; #[1,3,1] = 3;

..          Iteration. Used to create arithmetic sequences of numbers, especially in sets or tuples. Examples: {1..9}; [9,8..1];

:           "Such that". Used in set formers and tuple formers. Also used in quantified expressions.
Example: 
S := { x : x in {10..99} | x mod 6 = 0 };

|           Same as the colon.    exists x in S | x div 5 = 0;

$          Comment symbol. The rest of this line will not be processed.

%        Used to change a binary operation into something that works for an entire set or tuple. For instance, addition is a binary operation because you can only add two numbers at a time, like this: 1 + 2 = 3.  To add more than two numbers, put the % sign in front of the operator.
Examples:
%+{1..9} = 45; %max{1..9} = 9; %*{1..9} = 362880;
(The last example shows a nice way to do factorials.)