-constants might include `e` and `t`. "`'a`" is a type variable. The
-tick mark just indicates that the variable ranges over types rather
-than over values; in various discussion below and later, type variable
-can be distinguished by using letters from the greek alphabet
-(α, β, etc.), or by using capital roman letters (X, Y,
-etc.). "`τ1 -> τ2`" is the type of a function from expressions of
-type `τ1` to expressions of type `τ2`. And "`∀'a. τ`" is called a
-universal type, since it universally quantifies over the type variable
-`'a`. You can expect that in `∀'a. τ`, the type `τ` will usually
-have at least one free occurrence of `'a` somewhere inside of it.
+constants might include `e` and `t`. "α" is a type variable. In
+various discussions, type variables are distinguished by using letters
+from the greek alphabet (α, β, etc.), as we do here, or by
+using capital roman letters (X, Y, etc.), or by adding a tick mark
+(`'a`, `'b`, etc.), as in OCaml. "`τ1 -> τ2`" is the type of a
+function from expressions of type `τ1` to expressions of type `τ2`.
+And "`∀α.τ`" is called a universal type, since it universally
+quantifies over the type variable `α`. You can expect that in
+`∀α.τ`, the type `τ` will usually have at least one free occurrence of
+`α` somewhere inside of it.