concrete LettersCnc of Letters = {

  lincat L = Str ;
  lin 
    a = "a" ;
    b = "b" ;
    c = "c" ;
    d = "d" ;
    e = "e" ;
    f = "f" ;
    g = "g" ;
    h = "h" ;
    i = "i" ;
    j = "j" ;
    k = "k" ;
    l = "l" ;
    m = "m" ;
    n = "n" ;
    o = "o" ;
    p = "p" ;
    q = "q" ;
    r = "r" ;
    s = "s" ;
    t = "t" ;
    u = "u" ;
    v = "v" ;
    w = "w" ;
    x = "x" ;
    y = "y" ;
    z = "z" ;
}