Algorithm 4. Equivalence query EQ($\mathcal{H}$, $\mathcal{M}$).

Input: a hypothesis $\mathcal{H}$ and an abstract model $\mathcal{M}$

Output: a counterexample if $\mathcal{H}$ ≠ $\mathcal{M}$ , otherwise null

1: while true do

2:   find a word w that separates $\mathcal{H}$ and $\mathcal{M}$

3:   if w does not exist then

4:    return null

5:   end if

6:   if $\mathcal{M}$ .isAccepted(w) = MQ(w) then

7:    return w

8:   end if

9:   refine $\mathcal{M}$ with (w, MQ(w))

10: end while