reserve F for non empty TernaryFieldStr;
reserve a,b,c for Scalar of F;

theorem Th1:
  for u,u9,v,v9 being Real holds u <> u9 implies ex x being Real st
  u*x+v = u9*x+v9
proof
  let u,u9,v,v9 be Real;
  set x = (v9 - v)/(u - u9);
  assume u <> u9;
  then u - u9 <> 0;
  then
A1: (u - u9)*x = v9 - v by XCMPLX_1:87;
  reconsider x as Real;
  take x;
  thus thesis by A1;
end;
