PROGRAM MAIN
    IMPLICIT NONE
    INTEGER :: H, W, I, J, K, COUNT, X, Y, DX, DY
    CHARACTER*50, ALLOCATABLE, DIMENSION(:) :: S
    INTEGER, ALLOCATABLE, DIMENSION(:, :) :: S_NUM
    INTEGER, ALLOCATABLE, DIMENSION(:) :: U, V

    READ *, H, W
    ALLOCATE(S(H))
    ALLOCATE(S_NUM(H, W))
    S_NUM = 0
    READ *, S
    DO I = 1, H
        DO J = 1, W
            IF (S(I)(J:J) == '#') THEN
                S_NUM(I, J) = 1
            END IF
        END DO
    END DO

    K = SUM(S_NUM)
    ! PRINT *, K

    IF (MOD(K, 2) == 1) THEN
        PRINT *, 'NO'
        RETURN
    END IF

    ALLOCATE(U(K))
    ALLOCATE(V(K))

    COUNT = 1
    DO I = 1, H
        DO J = 1, W
            IF(S_NUM(I, J) == 1) THEN
                U(COUNT) = I
                V(COUNT) = J
                COUNT = COUNT + 1
            END IF
        END DO
    END DO

    ! PRINT *, U
    ! PRINT *, V

    DO I = 2, K
        DX = U(I) - U(1)
        DY = V(I) - V(1)
        COUNT = 0

        DO J = 1, K
            X = U(J) + DX
            Y = V(J) + DY
            IF ((X < 1 .OR. X > H) .OR. (Y < 1 .OR. Y > W)) THEN
                CYCLE
            END IF
            IF(S_NUM(X, Y) == 1) THEN
                COUNT = COUNT + 1
                S_NUM(X, Y) = 2
            END IF
        END DO

        IF (2 * COUNT == K) THEN
            PRINT *, 'YES'
            RETURN
        END IF
        DO J = 1, K
            IF(S_NUM(U(J), V(J)) == 2) S_NUM(U(J), V(J)) = 1
        END DO
    END DO

    PRINT *, 'NO'

END PROGRAM MAIN