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Otherwise, fastWP gets splitted back to classical right away.

turns out, Alt-Ergo really dislikes unsplitted premises

Prevent introduce_premises from splitting too aggressively
on the left-hand side:

- under quantifiers:
    "forall x. P /\ Q" =/=> "(forall x. P) /\ (forall x. Q)"

- match-with:
    "match t with A -> P | B -> Q" =/=> "(t = A -> P) /\ (t = B -> Q)"

- if-then-else:
    "if f then P else Q" =/=> "(f -> P) /\ (not f -> Q)"

- equivalence:
    "P <-> Q" =/=> "(P -> Q) /\ (Q -> P)"

Those splits duplicate formulas, hinder readability and do not
really simplify anything. Moreover, in case of a split under
a quantifier, they create several universal premises for provers
to instantiate, instead of just one.

TODO: introduce_premises should be able to split under
a single-branch match. However, this requires special
treatment in Introduce.dequant, since the pattern
should be rather skolemized than used as a condition.

Let's see if this helps our provers to instantiate the axiom.

Instead, we put a "stop_split" over the subsequent postcondition
under the (begin > end + 1) assumption. When this assumption is
unrealizable (strict for), this allows us to discharge the whole
branch as a single goal.

We will want to use stop_split higher in the VC formulas.

Conflicts:
	examples/fibonacci.mlw
	examples/fibonacci/why3session.xml
	examples/fibonacci/why3shapes.gz
	examples/koda_ruskey/why3session.xml
	examples/koda_ruskey/why3shapes.gz
	examples/schorr_waite_via_recursion/why3session.xml
	examples/schorr_waite_via_recursion/why3shapes.gz
	examples/tests-provers/bv/why3session.xml
	examples/tests-provers/bv/why3shapes.gz
	examples/tests-provers/ieee_float/why3session.xml
	examples/tree_of_array/why3session.xml
	examples/tree_of_array/why3shapes.gz
	examples/vstte12_bfs/why3session.xml
	examples/vstte12_bfs/why3shapes.gz
	theories/int.why
	theories/real.why

The underlying Monoid does not need to be commutative,
and is indeed not in example fibonacci.mlw