Fix a typo.

content/lambda-calculus/lambda-definability/introduction.tex

@@ -39,7 +39,7 @@
 represents a function accepting two arguments $f$ and $x$, and
 returns $f^n(x)$. Church numerals are evidently in normal form.
 
-A represention of natural numbers in the lambda calculus is only
+A representation of natural numbers in the lambda calculus is only
 useful, of course, if we can compute with them.  Computing with Church
 numerals in the lambda calculus means applying a $\lambd$-term~$F$ to
 such a Church numeral, and reducing the combined term~$F\, \num n$ to
@@ -48,7 +48,7 @@
 of the computation as being the number~$m$. We can then think of~$F$
 as defining a function $f\colon \Nat \to \Nat$, namely the function
 such that $f(n) = m$ iff $F\, \num n \red \num m$. Because of the
-Church-Rosser property, normal forms are unique if they exist. So if
+Church--Rosser property, normal forms are unique if they exist. So if
 $F\, \num n \red \num m$, there can be no other term in normal form,
 in particular no other Church numeral, that $F \, \num n$ reduces to.