This symbol represents a function with two arguments,
the first of which is a natural number and the second of which is a list.
The first argument is the length of the list.
This symbol represents a binary function whose first argument should be a list
L and whose second argument should be a positive integer i such that
the absolute value of i is in the interval [1..n], where n is the length of L.
If i is positive, it returns the i-th entry L[i] of L, if i is negative it
returns
the (n+1-i)-th entry of L.
This symbol takes two arguments both a list. It represents a function which returns a list made up of all
the elements of the first list which are not in the second.
Example:
Specification of the list [1,..,6], apart from the first 3 elements.
This symbol takes two lists as arguments, L and M say. The second argument is a
list containing only entries from [1..n], where n is the length of
L. The symbol represents the
function which returns a list whose length is equal to the length of
M, and having at position k the value of L at position M_k.