All admissible \(3\)-\((v,4,\lambda)\) directed designs exist
The authors show that a simple \(3\)-\((v,4,2)\) directed design exists for all values of \(v\). This shows that the necessary condition \(\lambda v\equiv 0\pmod 2\) for the existence of a \(3\)-\((v,4,\lambda)\) directed design is also sufficient.
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