Variables are defined dynamically. When you log in to a system, no variables are defined. The course of your program will define variables via the READ $($R$)$ and SET $($S$)$ commands, and undefine variables via the KILL $($K$)$ command. Notice that commands can be abbreviated to one letter.

As you know, there are two kinds of variables: string and numeric. A variable may be defined via a READ command, in which case it is automatically a string. The other way a variable can be defined is by the SET command which can define it as either string or numeric.

The syntax for the SET command is:

S argl,arg$2...$argx

The statement

S VAR$=$EXP

replaces $($or defines$)$ the variable VAR with the value of the expression EXP. The data type of VAR is determined by the expression.

Question. If I execute the following code

R Z S X$=$Z$,$Y$=$X

what type of variables are X$,$ Y and Z$?$

$1.$ All numeric

$2.$ All string

$3.$ X$,$ Y numeric; Z string

$4.$ X numeric; Y$,$ Z string

$5.$ X numeric; Y$,$ Z undefined

$6.$ Can$$t tell without more information