Duplicated critical pair

[fblanqui]

constant symbol A : TYPE;
constant symbol a : A;
symbol f : A → A;

rule f $x ↪ $x;
rule f _ ↪ a;

[/home/blanqui/src/lambdapi/tmp/dup_cp.lp:6:0-13]
Unjoinable critical pair:
t ≔ f $0
t ↪[] a ↪* a
  with f $0' ↪ a
t ↪[] $0 ↪* $0
  with f $0 ↪ $0
[/home/blanqui/src/lambdapi/tmp/dup_cp.lp:6:0-13]
Unjoinable critical pair:
t ≔ f $0
t ↪[] $0 ↪* $0
  with f $0 ↪ $0
t ↪[] a ↪* a
  with f $0 ↪ a