reserve f for non constant standard special_circular_sequence,
  i,j,k,i1,i2,j1,j2 for Nat,
  r,s,r1,s1,r2,s2 for Real,
  p,q for Point of TOP-REAL 2,
  G for Go-board;

theorem Th9:
  i >= 1 & j >= 1 & i+j = len f implies left_cell(Rev f,i) = right_cell(f,j)
proof
A1: len Rev f = len f by FINSEQ_5:def 3;
  Rev Rev f = f;
  hence thesis by A1,Th8;
end;
