rm prob (wip)

[affeldt-aist]

@t6s @hoheinzollern

[t6s]

TODO: cleaning and doc

[t6s]

I did some cleaning and will stop here.
Commit 890ab22 contains some breaking changes. Please check.

[t6s]

one remaining concern I could not resolve was remaining occurrences of prob_le1 and prob_ge0,
used in the form of have :=prob_le1 .., which could not be cleanly translated to have := le1 .. because of
an additional unification parameter in the latter.