reserve s for set,
  i,j for natural Number,
  k for Nat,
  x,x1,x2,x3 for Real,
  r,r1,r2,r3,r4 for Real,
  F,F1,F2,F3 for real-valued FinSequence,
  R,R1,R2 for Element of i-tuples_on REAL;

theorem
  for R1, R2 being complex-valued Function st -R1 = -R2 holds R1 = R2
proof
  let R1, R2 be complex-valued Function;
  assume -R1 = -R2;
  hence R1 = --R2 .= R2;
end;
