Thirteen is at least the difference of a number v and 1

Learn the rules:

"at least" means "greater than or equal to".
"at most" means "less than or equal to".

Thirteen is at least the difference of a number v and 1

(Thirteen)        (is at least)          (the difference of a number v and 1)
     |                |                                  |
[Thirteen] (is greater than or equal to) (the difference of a number v and 1)
     |                |                                  |
     |                |                                  |
    13                ≥                                 v-1

                   13 ≥ v-1
                   +1    +1      <-- add +1 to both sides
                  ---------
                   13 ≥ v

Edwin