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## 36.2 Definitions for Lists

Function: APPEND (list1, list2, ...)
returns a single list of the elements of list1 followed by the elements of list2,... APPEND also works on general expressions, e.g. APPEND(F(A,B), F(C,D,E)); -> F(A,B,C,D,E). Do EXAMPLE(APPEND); for an example.

Function: ATOM (exp)
is TRUE if exp is atomic (i.e. a number or name) else FALSE. Thus ATOM(5) is TRUE while ATOM(A[1]) and ATOM(SIN(X)) are FALSE. (Assuming A[1] and X are unbound.)

Function: CONS (exp, list)
returns a new list constructed of the element exp as its first element, followed by the elements of list. CONS also works on other expressions, e.g. CONS(X, F(A,B,C)); -> F(X,A,B,C).

Function: COPYLIST (L)
creates a copy of the list L.

Function: DELETE (exp1, exp2)
removes all occurrences of exp1 from exp2. Exp1 may be a term of exp2 (if it is a sum) or a factor of exp2 (if it is a product).
 ```(C1) DELETE(SIN(X),X+SIN(X)+Y); (D1) Y + X ```
DELETE(exp1, exp2, integer) removes the first integer occurrences of exp1 from exp2. Of course, if there are fewer than integer occurrences of exp1 in exp2 then all occurrences will be deleted.

Function: ENDCONS (exp, list)
returns a new list consisting of the elements of list followed by exp. ENDCONS also works on general expressions, e.g. ENDCONS(X, F(A,B,C)); -> F(A,B,C,X).

Function: FIRST (exp)
yields the first part of exp which may result in the first element of a list, the first row of a matrix, the first term of a sum, etc. Note that FIRST and its related functions, REST and LAST, work on the form of exp which is displayed not the form which is typed on input. If the variable INFLAG [FALSE] is set to TRUE however, these functions will look at the internal form of exp. Note that the simplifier re-orders expressions. Thus FIRST(X+Y) will be X if INFLAG is TRUE and Y if INFLAG is FALSE. (FIRST(Y+X) gives the same results).

Function: GET (a, i)
retrieves the user property indicated by i associated with atom a or returns FALSE if a doesn't have property i.
 ```(C1) PUT(%E,'TRANSCENDENTAL,'TYPE); (D1) TRANSCENDENTAL (C2) PUT(%PI,'TRANSCENDENTAL,'TYPE)\$ (C3) PUT(%I,'ALGEBRAIC,'TYPE)\$ (C4) TYPEOF(EXP) := BLOCK([Q], IF NUMBERP(EXP) THEN RETURN('ALGEBRAIC), IF NOT ATOM(EXP) THEN RETURN(MAPLIST('TYPEOF, EXP)), Q : GET(EXP, 'TYPE), IF Q=FALSE THEN ERRCATCH(ERROR(EXP,"is not numeric.")) ELSE Q)\$ (C5) TYPEOF(2*%E+X*%PI); X is not numeric. (D5) [[TRANSCENDENTAL, []], [ALGEBRAIC, TRANSCENDENTAL]] (C6) TYPEOF(2*%E+%PI); (D6) [TRANSCENDENTAL, [ALGEBRAIC, TRANSCENDENTAL]] ```
Function: LAST (exp)
yields the last part (term, row, element, etc.) of the exp.

Function: LENGTH (exp)
gives (by default) the number of parts in the external (displayed) form of exp. For lists this is the number of elements, for matrices it is the number of rows, and for sums it is the number of terms. (See DISPFORM). The LENGTH command is affected by the INFLAG switch [default FALSE]. So, e.g. LENGTH(A/(B*C)); gives 2 if INFLAG is FALSE (Assuming EXPTDISPFLAG is TRUE), but 3 if INFLAG is TRUE (the internal representation is essentially A*B^-1*C^-1).

Variable: LISTARITH
default: [TRUE] - if FALSE causes any arithmetic operations with lists to be suppressed; when TRUE, list-matrix operations are contagious causing lists to be converted to matrices yielding a result which is always a matrix. However, list-list operations should return lists.

Function: LISTP (exp)
is TRUE if exp is a list else FALSE.

Function: MAKELIST (exp,var,lo,hi)
returns a list as value. MAKELIST may be called as MAKELIST(exp,var,lo,hi) ["lo" and "hi" must be integers], or as MAKELIST(exp,var,list). In the first case MAKELIST is analogous to SUM, whereas in the second case MAKELIST is similar to MAP. Examples:
 ``` MAKELIST(CONCAT(X,I),I,1,6) yields [X1,X2,X3,X4,X5,X6] MAKELIST(X=Y,Y,[A,B,C]) yields [X=A,X=B,X=C] ```

Function: MEMBER (exp, list)
returns TRUE if exp occurs as a member of list (not within a member). Otherwise FALSE is returned. Member also works on non-list expressions, e.g. MEMBER(B, F(A,B,C)); -> TRUE.

Function: REST (exp, n)
yields exp with its first n elements removed if n is positive and its last -n elements removed if n is negative. If n is 1 it may be omitted. Exp may be a list, matrix, or other expression.

Function: REVERSE (list)
reverses the order of the members of the list (not the members themselves). REVERSE also works on general expressions, e.g. REVERSE(A=B); gives B=A. REVERSE default: [FALSE] - in the Plotting functions, if TRUE cause a left-handed coordinate system to be assumed.

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