There is a KILL command which removes a variable and its value from the symbol table, thus undefining it$.$ The syntax for the KILL is:

K A KILL command followed by $2$ spaces kills all variables. K VAR The variable VAR is killed, if it exists.

K $($VAR$,$VAS$)$ All variables except VAR and VAS are killed.

The most common use of KILL is to free storage space. Another use is to flag conditions $-$ if a particular value is defined, that means one thing; and if it is undefined, that means something else.

Question: K S S$="4",$T$=$S$+2,$Z$=$T$>6$ K K$,$ J$,$ S