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

examples of 1 level patterns:

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

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

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

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

@ @ @    @ @ @
@ 7 @ -> @ 7 @
. @ @    _ @ @

etc