--- upto(max) {|s| ... }

    self Ϥ max ޤǡּʸפ֤˥֥å
    ͿƷ֤ޤּפˤĤƤ String#succ [String/succ] 
    ȤƤ

    Υ᥽åɤʸ Range ǻѤޤ
    

    ȤаʲΥɤ a, b, c, ... z,aa, ... az, ..., za 
    Ϥޤ

           ("a" .. "za").each do |str|
             puts str
           end

