[isabelle] how to use brackets in lemma

failed to parse lemma when prove the following
would like to see any further usage when continuing adding letters into it
lemma mfold5 [simp]:"mfold5 f [a,b,c,d,e] x = f e (f d (f c (f b (f a x))))"
lemma mfold [simp]:"mfold f [a,b,c] x = f c (f b (f a x))"apply(simp_all)apply(auto)donelemma mfoldr [simp]:"mfoldr f [a,b,c] x = f a (f b (f c x))"apply(induct_tac x)apply(auto)donelemma mfoldl [simp]:"mfoldl f x [a,b,c] = f (f (f x a) b) c"apply(induct_tac x)apply(auto)done

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