for d9 being Nat for d being non zeroNat for G being Grating of d st d = d9 + 1 holds for A being Subset of (REAL d) holds ( A incells (d9,G) iff ex l, r being Element of REAL d ex i0 being Element of Seg d st ( A =cell (l,r) & l . i0 = r . i0 & l . i0 in G . i0 & ( for i being Element of Seg d st i <> i0 holds ( l . i < r . i & [(l . i),(r . i)] is Gap of G . i ) ) ) )