Goal:
    A : Type  x : A  m1 : tree' A  m2 : tree' A  H : xH <> xH
  ============================
   (Some x = None)


DEBUG:Going to execute:
congruence
DEBUG LTAC Evaluated term: gso0
Level 0: Backtrace:

In environment
A : Type
x : A
m1, m2 : tree' A
H : xH <> xH
Unable to unify "get' ?M1985 (set0 ?M1986 ?M1987) = None" with
 "Some x = None".
Level 0: Backtrace:

In environment
A : Type
x : A
m1, m2 : tree' A
H : xH <> xH
Unable to unify "get' ?M1985 (set0 ?M1986 ?M1987) = None" with
 "Some x = None".