{{\mathcal O}}&{{\mathcal O}}\end{bmatrix}$$ In this case $|[0,2{\vec c}]|=17$ and the endomorphism algebra is given by $$\begin{xy} 0;<3.5pt,0pt>:<0pt,3.5pt>::
(-60,0) *+{P} ="0",
(-30,30) *+{P({\vec x}_1)} ="1",
(-30,10) *+{P({\vec x}_2)} ="2",
(-30,-10) *+{P({\vec x}_3)} ="3",
(-30,-30) *+{P({\vec x}_4)} ="4",
(0,40) *+{P({\vec x}_1+{\vec x}_2)} ="12",
(0,20) *+{P({\vec x}_1+{\vec x}_3)} ="13",
(0,10) *+{P({\vec x}_1+{\vec x}_4)} ="14",
(0,-10) *+{P({\vec x}_2+{\vec x}_3)} ="23",
(0,-20) *+{P({\vec x}_2+{\vec x}_4)} ="24",
(0,-40) *+{P({\vec x}_3+{\vec x}_4)} ="34",
(0,0) *+{P({\vec c})} ="c",
(30,30) *+{P({\vec x}_1+{\vec c})} ="c1",
(30,10) *+{P({\vec x}_2+{\vec c})} ="c2",
(30,-10) *+{P({\vec x}_3+{\vec c})} ="c3",
(30,-30) *+{P({\vec x}_4+{\vec c})} ="c4",
(60,0) *+{P(2{\vec c})} ="2c",
"0", {\ar"1"|{x_1}},
"0", {\ar"2"|{x_2}},
"0", {\ar"3"|{x_3}},
"0", {\ar"4"|{x_4}},
"1", {\ar"c"|(.3){x_1}},
"1", {\ar"12"|(.3){x_2}},
"1", {\ar"13"|(.3){x_3}},
"1", {\ar"14"|(.3){x_4}},
"2", {\ar"12"|(.4){x_1}},
"2", {\ar"c"|(.4){x_2}},
"2", {\ar"23"|(.4){x_3}},
"2", {\ar"24"|(.4){x_4}},
"3", {\ar"13"|(.3){x_1}},
"3", {\ar"23"|(.3){x_2}},
"3", {\ar"c"|(.3){x_3}},
"3", {\ar"34"|(.3){x_4}},
"4", {\ar"14"|(.4){x_1}},
"4", {\ar"24"|(.4){x_2}},
"4", {\ar"34"|(.4){x_3}},
"4", {\ar"c"|(.4){x_4}},
"12", {\ar"c2"|(.6){x_1}},
"12", {\ar"c1"|(.7){x_2}},
"13", {\ar"c3"|(.7){x_1}},
"13", {\ar"c1"|(.7){x_3}},
"14", {\ar"c4"|(.6){x_1}},
"14", {\ar"c1"|(.7){x_4}},
"23", {\ar"c3"|(.7){x_2}},
"23", {\ar"c2"|(.6){x_3}},
"24", {\ar"c4"|(.6){x_2}},
"24", {\ar"c2"|(.6){x_4}},
"34", {\ar"c4"|(.6){x_3}},
"34", {\ar"c3"|(.7){x_4}},
"c", {\ar"c1"|(.7){x_1}},
"c", {\ar"c2"|(.6){x_2}},
"c", {\ar"c3"|(.7){x_3}},
"c", {\ar"c4"|(.6){x_4}},
"c1", {\ar"2c"|{x_1}},
"c2", {\ar"2c"|{x_2}},
"c3", {\ar"2c"|{x_3}},
"c4", {\ar"2c"|{x_4}},
\end{xy}$$ with relations: $$\begin{aligned}
    x_ix_j&=x_jx_i\\
    x_4^2&=x^2_1+x_2^2+x_3^2\end{aligned}$$

[10]{} Artin, M.; Zhang, J. J. *Noncommutative projective schemes*. Adv. Math. 109 (1994), no. 2, 228–287 D. Baer, *Tilting sheaves 