let regexp num = digit+
let regexp tex_token = '\\' alpha+
let regexp symbol = [^ 'a' - 'z' 'A' - 'Z' '0' - '9' ' ' '\t' '\n' ]
-let regexp ident_cont = alpha | num | '_'
+let regexp ident_cont = alpha | num | '_' | '\''
let regexp ident_cont' = ident_cont | tex_token
let regexp ident = (alpha ident_cont*) | ('_' ident_cont+)
let regexp ident' = ((alpha | tex_token) ident_cont'*) | ('_' ident_cont'+)