Lambda expressions that have no free variables are known as **combinators**. Here are some common ones:
-<pre>
-**I** is defined to be `\x x`<p>
-**K** is defined to be `\x y. x`, That is, it throws away its second argument. So `K x` is a constant function from any (further) argument to `x`. ("K" for "constant".) Compare K to our definition of **true**.<p>
-**get-first** was our function for extracting the first element of an ordered pair: `\fst snd. fst`. Compare this to K and true as well.<p>
-**get-second** was our function for extracting the second element of an ordered pair: `\fst snd. snd`. Compare this to our definition of false.<p>
-**ω** is defined to be: `\x. x x`<p>
-</pre>
+> **I** is defined to be `\x x`
+
+> **K** is defined to be `\x y. x`, That is, it throws away its second argument. So `K x` is a constant function from any (further) argument to `x`. ("K" for "constant".) Compare K to our definition of **true**.
+
+> **get-first** was our function for extracting the first element of an ordered pair: `\fst snd. fst`. Compare this to K and true as well.
+
+> **get-second** was our function for extracting the second element of an ordered pair: `\fst snd. snd`. Compare this to our definition of false.
+
+> **ω** is defined to be: `\x. x x`
It's possible to build a logical system equally powerful as the lambda calculus (and readily intertranslatable with it) using just combinators, considered as atomic operations. Such a language doesn't have any variables in it: not just no free variables, but no variables at all.