The main type of terms, that contains symbols, applications, binary and unary operators.

The table is used to store available operators.

get_unary tbl t returns the priority, or binding power of operator identified t if it is a unary operator, or None.

get_binary tbl t returns the priority (or binding power) and associativity of operator t, or None if t isn't a binary operator.

make_appl tbl t u returns the application of t to u, sometimes noted @(t, u), or just t u, with tbl being the table of operators.