Pascal Report  149  Identifiers serve to denote constants, types, variables, procedures,  functions,  fields, and bounds.  Directives are used in procedure and  function declarations.  The  spelling  of a word symbol, identifier, or directive is the entire  sequence of specific letters and digits that it contains. No identifier  or  directive may have the same spelling as a word symbol.  Identifier  =  Letter  I  Letter  I  Digit} .  Directive  =  Letter  I  Letter  I  Digit} .  Many ofthe symbols are constructed from letters and digits. Except  within  a character  string,  a lower-case  letter  is  equivalent  to  the  corresponding upper-case letter.  The following alternative representations are standard:  SpecialSymhol  =  "+" I "-" I  "*"  I  "I"  I  "="  I "<>" I "<"  I "<=" I ">"  I ">=" I  "(" I ")" I "[" I "]" I  ":="  I "." I " .. " I  " :" I ";" I  "i"  I  WordSymhol.  WordSymhol  =  "di v" I "mod" I "nil" I "in" I "or" I "and" I  "not"I"if"I"then"I"else"I"case"I"of"l  "repeat" I "until" I "while" I "do" I "for" I  "to" I "goto" I "downto" I "begin" I "end" I  "with" I "const" I "var" I "type" I "array" I  "record" I "set" I "file" I "function" I  "procedure" I "label" I "packed" I "program" .  Reference  Alternative  i  ( .  .  )  or  @  Letter  =  "a" I "b" I "c" I "d" I "e" I "f" I "g" I "h" I "i" I  "j"I"k"I"l"I"m"I"n"I"o"I"p"I"q"I"r"l  "s"I"t"I"u"I"v"I"w"I"x"I"y"I"z" .  Digit  =  "0" I "1" I "2" I "3" I "4" I "5" I "6" I "7" I "8" I "9" . 