[STATEMENT]
lemma absn_cong[intro]: "s \<leftrightarrow> t \<Longrightarrow> (Abs^^n) s \<leftrightarrow> (Abs^^n) t"
[PROOF STATE]
proof (prove)
goal (1 subgoal):
 1. s \<leftrightarrow> t \<Longrightarrow> (Abs ^^ n) s \<leftrightarrow> (Abs ^^ n) t
[PROOF STEP]
by (induction n) auto