intuition.
rewrite bool_Comp_seq.
assert (Pr  [b2 <-$ c2; ret true || b2 ] == 1).
comp_irr_l.
rewrite evalDist_ret_1; simpl; intuition.
rewrite H0.
clear H0.
assert (Pr  [b2 <-$ c2; ret false || b2 ] == Pr[c2]).
rewrite bool_Comp_seq.
rewrite evalDist_ret_1.
rewrite evalDist_ret_0.
rewrite ratMult_0_r.
rewrite <- ratAdd_0_r.
eapply ratMult_1_r.
simpl.
intuition.
simpl; intuition.
rewrite H0.
clear H0.
rewrite ratMult_1_r.
intuition.
Qed.

Theorem evalDist_right_ident_eqb :
forall (A : Set)(eqd : EqDec A)(c : Comp A)(a : A),
Pr[x <-$ c; ret (eqb a x)] == evalDist c a.