4-rings or 4-squares puzzle

You are encouraged to solve this task according to the task description, using any language you may know.
Task

Replace       a, b, c, d, e, f,   and
  g        with the decimal
digits   LOW   ───►   HIGH

such that the sum of the letters inside of each of the four large squares add up to
the same sum.

            ╔══════════════╗      ╔══════════════╗
            ║              ║      ║              ║
            ║      a       ║      ║      e       ║
            ║              ║      ║              ║
            ║          ┌───╫──────╫───┐      ┌───╫─────────┐
            ║          │   ║      ║   │      │   ║         │
            ║          │ b ║      ║ d │      │ f ║         │
            ║          │   ║      ║   │      │   ║         │
            ║          │   ║      ║   │      │   ║         │
            ╚══════════╪═══╝      ╚═══╪══════╪═══╝         │
                       │       c      │      │      g      │
                       │              │      │             │
                       │              │      │             │
                       └──────────────┘      └─────────────┘

Show all output here.



   Show all solutions for each letter being unique with
        LOW=1     HIGH=7

   Show all solutions for each letter being unique with
        LOW=3     HIGH=9

   Show only the   number   of solutions when each letter can be non-unique
        LOW=0     HIGH=9



Related task

 Solve the no connection puzzle


fspuz=:dyad define
  range=: x+i.1+y-x
  lo=. 6+3*x
  hi=. _3+2*y
  r=.i.0 0
  if. lo <: hi do.
    for_T.lo ([+[:i.1+-~) hi do.
      range2=: (#~ (T-{.range)>:]) range
      range3=: (#~ (T-+/2{.range)>:]) range
      ab=: (#~ ~:/"1) (,.T-])range2
      abc=: ;ab <@([ ,"1 0 -.~)"1/range3
      abcd=: (#~ T = +/@}."1) ;abc <@([ ,"1 0 -.~)"1/range3
      abcde=: ;abcd <@([ ,"1 0 -.~)"1/range3
      abcdef=: (#~ T = +/@(3}.])"1) ;abcde <@([ ,"1 0 -.~)"1/range3
      abcdefg=: (#~ T = +/@(5}.])"1) ;abcdef <@([ ,"1 0 -.~)"1/range2
      r=.r,(#~ x<:<./"1)(#~ y>:>./"1)abcdefg
    end.
  end.
)