reserve F for non empty TernaryFieldStr;
reserve a,b,c for Scalar of F;
reserve F for Ternary-Field;
reserve a,a9,b,c,x,x9,u,u9,v,v9,z for Scalar of F;

theorem
  a<>0.F implies for b,c ex x st Tern(a,x,b) = c
proof
  assume
A1: a <> 0.F;
  let b,c;
  consider x such that
A2: Tern(a,x,b) = Tern(0.F,x,c) by A1,Def5;
  take x;
  thus thesis by A2,Def5;
end;
