(a.) Fourfold; folded or doubled twice.

Photostat Xerox biquadrate biquadratic clone copy counterpart ditto double dupe duplicate duplication facsimile fourfold hectograph make four manifold microcopy microfilm mimeo mimeograph model multigraph multiply by four quadrable quadrigeminal quadruple quadruplex reduplicate repetition replica replicate replication representation reproduce reproduction stat tetraploid trace transcribe triplicate