Verb fold up has 2 senses
  1. fold, fold up, turn up - bend or lay so that one part covers the other; "fold up the newspaper"; "turn up your collar"
    --1 is one way to change surface
    Sample sentence:
    They fold up the sheets
  2. fold, fold up - become folded or folded up; "The bed folds in a jiffy"
    --2 is one way to change
    Sample sentences:
    The sheets didn't fold up
    These fabrics fold up easily
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