# unfreeze allows adding variables beyond the original data frame columns
data(tpc_example)
kn <- knowledge(tpc_example)
# this would error while frozen
try(add_vars(kn, "new_var"))
# unfreeze and add the new variable successfully
kn <- unfreeze(kn)
kn <- add_vars(kn, "new_var")
print(kn)
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