\mathcal - Used to turn on calligraphic font for uppercase letters and digits.
{ \mathcal #1 }
\mathcal command is used to turn on calligraphic font for uppercase letters and digits.
\mathcal{ABCDEFGHIJKLMNOPQRSTUVWXYZ}
\mathcal{0123456789}
\mathcal{abcdefghijklmnopqrstuvwxyz}
abcdefghijklmnopqrstuvwxyz
\mathcal{AB}AB