The Empty Symbol
Description
Examples
``
The empty symbol can be expressed by a pair of left single quotes with no enclosed characters (not even a blank).
The following is a valid assignment statement to input to Maple.
`` := 99;
No characters are printed as the representation of this name.
The empty symbol has various special uses within Maple. Hence, if the empty symbol has been assigned in the above manner, strange behavior is to be expected from several Maple functions, most notably ifactor.
A common use of the empty symbol is to display expressions in an unsimplified form, which Maple would normally automatically simplify. It can also display variables with their values substituted, in unsimplified form. In this way, it can be used in a similar manner to ifactor. See examples below.
Notes: The empty symbol is quite different from the value of the global variable NULL, which is the null expression sequence. However, the output form for each consists of zero printed characters.
The empty symbol is a symbol, while the empty string is a string. The empty string is input and printed as "", while the empty symbol is input as `` and not printed. The empty string cannot be assigned to, while the empty symbol can.
$\mathrm{restart}$
$a\u2254\mathrm{``}$
${a}{\u2254}$
$b\u2254\mathrm{NULL}$
$c\u2254''''$
${c}{\u2254}{''''}$
$\left[a\,b\,c\right]$
$\left[{\,}{''''}\right]$
$\mathrm{nops}\left(\right)$
${2}$
$\left[1\,a\,3\right]$
$\left[{1}{\,}{\,}{3}\right]$
$\left[1\,b\,3\right]$
$\left[{1}{\,}{3}\right]$
The empty symbol can be used to display unsimplified math and formulae with values substituted. Note the difference between using the empty symbol and quotes.
``(2)*``(3);
$\left({2}\right){}\left({3}\right)$
expand((7));
${6}$
x:=2;
${x}{\u2254}{2}$
y:=3;
${y}{\u2254}{3}$
3*``(x)+2*``(y);
${3}{}\left({2}\right){+}{2}{}\left({3}\right)$
"3*(x)+2*(y)";
${''3*(x)+2*(y)''}$
3*x+2*y;
${12}$
See Also
names
NULL
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