Variable t seems to have a special property: You can draw a line by writing
(1+2t, 3+4t, 5+6t)
on command line.
But if t is already in use, e.g. t = 0, you get only a point, in this case
(1, 3, 5).
So, here is my question: how can you "undefine" a variable? Is the the only solution not to use t as a variable?
(It would be nice to be able to draw a plane with same way, e.g. (1+2t+3s,4+5t+6s,7+8t+9t).)