legend: _ = safe square
        . = unknown
        @ = mine
        0-9 = corresponding number

examples of deeper patterns

. . . . .    _ @ _ @ _
. 1 2 1 . -> _ 1 2 1 _
. _ _ _ .    _ _ _ _ _

. . . . . .    _ _ . . . _
. 2 . 3 1 . -> _ 2 . 3 1 _
. . . . . .    _ _ . . . _


. . . .    @ . . _
. 3 1 . -> . 3 1 _
. 1 . .    . 1 _ _
. . . .    _ _ _ .

. . . _    _ . . _
. 2 2 . -> . 2 2 @
. 2 _ _    . 2 _ _
_ . _      _ @ _