Fig. 4
![Fig. 4](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs42787-020-0068-z/MediaObjects/42787_2020_68_Fig4_HTML.png)
The k-the projection (k=1,2,3). This figure explained and compute the 3-polar fuzzy set \( \overline{\mathcal{A}}\in {\left({\left[0,60\right]}^3\right)}^X \), defined by \( {p}_k{}^{\circ}\overline{\mathcal{A}}=60\wedge {\sum}_{i\in I}{p}_k{}^{\circ}\mathcal{A}(x)\kern1.25em \left(\forall x\in X\right),\kern0.5em \) where pk : [0, 60]3 → [0, 60] is the k-the projection (k=1,2,3)