Goal:
  
  G : t
  HI : invariants
  A : Prop
  B : Prop
  b : B
  H0 : A -> B
  H1 : B -> A
  ============================
   A


DEBUG:Going to execute:
assert X2
Level 1: evaluation returns
assert X2; [ exact (id0 id1) | clear id0 ]
where
id1 := b
of type
intropattern
id0 := H1
of type
intropattern
flags := 
of type
tauto_flags
X2 := A
of type
constr of type tacvalue