:: deftheorem Def3 defines mid FINSEQ_6:def 3 :
for f being FinSequence
for k1, k2 being Nat holds
( ( k1 <= k2 implies mid (f,k1,k2) = (f /^ (k1 -' 1)) | ((k2 -' k1) + 1) ) & ( not k1 <= k2 implies mid (f,k1,k2) = Rev ((f /^ (k2 -' 1)) | ((k1 -' k2) + 1)) ) );