It is common in mathematics to use subscripted variables. We use the underscore to represent subscripts. If we haven't assigned a value to x we may simply start using it as a subscripted variable. The subscripts can be anything.
i1 : x |
i2 : x_4 |
i3 : x_(2,3) |
The .. operator knows what to do with subscripted variables.
i4 : x_10 .. x_20 |
i5 : x_(1,1) .. x_(2,3) |
Values can be assigned to these variables with #.
i6 : x#10 = 555; |
i7 : x_10 |
Be careful not to assign a value to x itself if you wish to continue using it as a subscripted variable.
See also: