[func.require] Add missing formatting of subscript index (#7071)

Author: j6t

source/utilities.tex

@@ -10825,7 +10825,7 @@
 \item \tcode{(t$_1$.*f)(t$_2$, $\dotsc$, t$_N$)} when \tcode{f} is a pointer to a
 member function of a class \tcode{T}
 and
-\tcode{is_same_v<T, remove_cvref_t<decltype(t1)>> ||}
+\tcode{is_same_v<T, remove_cvref_t<decltype(t$_1$)>> ||}
 \tcode{is_base_of_v<T, remove_cvref_t<decltype(t$_1$)>>} is \tcode{true};
 
 \item \tcode{(t$_1$.get().*f)(t$_2$, $\dotsc$, t$_N$)} when \tcode{f} is a pointer to a
@@ -10839,7 +10839,7 @@
 \item \tcode{t$_1$.*f} when $N = 1$ and \tcode{f} is a pointer to
 data member of a class \tcode{T}
 and
-\tcode{is_same_v<T, remove_cvref_t<decltype(t1)>> ||}
+\tcode{is_same_v<T, remove_cvref_t<decltype(t$_1$)>> ||}
 \tcode{is_base_of_v<T, remove_cvref_t<decltype(t$_1$)>>} is \tcode{true};
 
 \item \tcode{t$_1$.get().*f} when $N = 1$ and \tcode{f} is a pointer to