def rotmap(start):
    """
    dict[char,char]: Map chars (from start to start+26) to rotated characters.
    """
    ints = range(start,start+26)
    rots = (
        start+i%26 for i in range(  13,  13 +26)
        )

    return dict( zip( map( chr,ints ),map( chr,rots ) ) )