normalize_lccn("n 78890351 ") # "n78890351"
normalize_lccn("###78890351#") # "78890351"
normalize_lccn(" 79139101 /AC/r932") # "79139101"
normalize_lccn("85-2 ") # "85000002"
normalize_lccn("85-2 ", allow.hyphens=FALSE) # NA
# vectorized
normalize_lccn(c("85-2 ", " 79139101 /AC/r932", "n 78890351 "))
# c("85000002", "79139101", "n78890351"))
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