Certain identifiers in HOL are reserved, e.g. `if', `let' and `|',
meaning that they are special to the parser and cannot be used as ordinary
identifiers. The call reserved_words() returns a list of such identifiers.
FAILURE CONDITIONS
Never fails.
EXAMPLE
In the default HOL state:
# reserved_words();;
val it : string list =
["("; ")"; "["; "]"; ""; ""; ":"; ";"; "."; "|"; "let"; "in"; "and";
"if"; "then"; "else"; "//"]