The rule of renju is not clear in terms of the definition of three. Basically, there are two different definitions of three:

Definition 1: A row with three stones to which you can add one more stone to attain a straight four.

Definition 2: A row with three stones to which you, without at the same time a five in a row is made, can add one more stone to attain a straight four.

Different definition, in some scenarios, leads to different judgement about forbidden moves. An example is d14e14c13c12d12a9c11e11f12g12f13n13h12n11i11e12. The judegment about forbidden moves according to definition 1 and 2, are shown in figure 1, and figure 2 respectively.

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Fig. 1

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Fig. 2

Definition 2 is used in the international rules of renju, though it is disputable.