To a friend

Dear friend, it has been two years since we last met, and I think of you more often than I write, which is not often enough.

Dear friend: $2$ years since we met. Thoughts of you ($f$) $>$ letters to you ($n$), and $n\ll$ enough.

friend: $\Delta t=2$ y. $f>n\ll$ enough.

You live six hundred kilometres away. The train takes five hours and costs about as much as three dinners out, so I can afford it twice a year.

Distance $=600$ km. Train: $5$ h, cost $\approx 3$ dinners $\Rightarrow$ affordable $2\times$ a year.

$d=600$ km. train: $5$ h, cost $\approx 3\cdot$ dinner $\Rightarrow 2$/year.

I promise this: before the summer ends, there will be a day on which I knock on your door. If you are away that day, I will wait for the next.

A promise: $\exists$ a day $d$ before the end of summer: on $d$ I knock on your door. You away on $d\Rightarrow$ I wait for $d+1$.

$\exists d<$ end of summer: knock$(d)$. away$(d)\Rightarrow$ wait$(d+1)$.

Until then, write when you can. One line from you is worth more than a hundred from strangers.

Until then: write when you can. $1$ line from you $>100$ from strangers.

write whenever $\exists$ time. $1\cdot$ line(you) $>100\cdot$ line(stranger).