<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def is_eyeish(board, c):
    'Check if c is an eye, for the purpose of restricting MC rollouts.'
    # pass is fine.
    if c is None:
        return
    color = is_koish(board, c)
    if color is None:
        return None
    diagonal_faults = 0
    diagonals = DIAGONALS[c]
    if len(diagonals) < 4:
        diagonal_faults += 1
    for d in diagonals:
        if not board[d] in (color, EMPTY):
            diagonal_faults += 1
    if diagonal_faults > 1:
        return None
    else:
        return color