how can we express the following correctly.
$$f:E\to F $$ $$E \subseteq C_1 \times C_2 \times C_3 \times C_4 $$
$$f|_A:A\to F$$ $$A \subseteq C_1 \times C_4 $$ here, I misused the notation of mathematical restriction. I am looking for some notation like $f|_A$