John & Freek, I'm sorry, I just goofed, I really want to get rid of
two lines of code, not just one.  Here's the last thm of
http://www.math.northwestern.edu/~richter/OpenIntervalHilbertAxiom.ml

let TwosidesTriangle2aLine_THM = thm `;
  let A B C be point;
  let l be point_set;
  assume Line l /\ ~Collinear (A,B,C) [H1];
  thus A,B same_side l \/ B,C same_side l \/ A,C same_side l

  proof
    (A,B same_side l \/ B,C same_side l) \/ A,C same_side l
    proof
      assume ~(A,B same_side l \/ B,C same_side l);
      ~(A,B same_side l) /\ ~(B,C same_side l) [H2] by -;
      [...] 

I think this should have worked:

  thus A,B same_side l \/ B,C same_side l \/ A,C same_side l

  proof
    assume  ~(A,B same_side l) /\ ~(B,C same_side l) [H2];
    [...] 

I would have thought that miz3 would understand that

alpha \/ beta \/ gamma 

is equivalent to 

~alpha /\ ~beta ==> gamma

It looks to me that I needed to tell miz3 two facts:

alpha \/ beta \/ gamma <=> (alpha \/ beta) \/ gamma 

~(alpha \/ beta) <=> ~alpha /\ ~beta

But I could easily be misunderstanding Mizar, miz3 and HOL Light.

-- 
Best,
Bill 

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