• Separate the effects with spaces.
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• Use a vertical bar (|) to create main effects and interactions. For example, A|B|C is the same as A B A*B C A*C B*C A*B*C.
• Use an at-sign (@) following the use of vertical bars to remove interaction terms. For example, A|B|C@2 removes the three-way interaction term from A|B|C.