M3[Z]={⎝⎛a11a21a31a12a22a32a13a23a33⎠⎞,aij∈Z}
Сonsider the basis
E11=⎝⎛100000000⎠⎞,E12=⎝⎛000100000⎠⎞,E13=⎝⎛000000100⎠⎞,E21=⎝⎛010000000⎠⎞,E22=⎝⎛000010000⎠⎞,E23=⎝⎛000000010⎠⎞,E31=⎝⎛001000000⎠⎞,E32=⎝⎛000001000⎠⎞,E33=⎝⎛000000001⎠⎞
A=⎝⎛a11a21a31a12a22a32a13a23a33⎠⎞=a11E11+a12E12++a13E13+a21E21+a22E22++a23E23+a31E31+a32E32++a33E33
Let's put together a Kelly table and we denote
O=⎝⎛000000000⎠⎞
E11E12E13E21E22E23E31E32E33E11E11OOE21OOE31OOE12E12OOE22OOE32OOE13E13OOE23OOE33OOE21OE11OOE21OOE31OE22OE12OOE22OOE32OE23OE13OOE23OOE33OE31OOE11OOE21OOE31E32OOE12OOE22OOE32E33OOE13OOE23OOE33
Let's show that A2=0
A2=(a11E11+a12E12++a13E13+a21E21+a22E22++a23E23+a31E31+a32E32++a33E33)(a11E11+a12E12++a13E13+a21E21+a22E22++a23E23+a31E31+a32E32++a33E33)==a112E11+a11a12E12++a11a13E13+a12a21E11+a12a22E12++a12a23E13+a13a31E11+a13a32E12++a13a33E13+
+a21a11E21+a21a12E22++a21a13E23+a22a21E21+a222E22++a22a23E23+a23a31E21+a23a32E22++a23a33E23++a31a11E31+a31a12E32++a31a13E33+a32a21E31+a32a22E32++a32a23E33+a33a31E31+a33a32E32++a332E33=
=(a112+a12a21+a13a31)E11++(a11a12+a12a22+a13a32)E12++(a11a13+a12a23+a13a33)E13=
+(a21a11+a22a21+a23a31)E21++(a21a12+a222+a23a32)E22++(a21a13+a22a23+a23a33)E23++(a31a11+a32a21+a33a31)E31++(a31a12+a32a22+a33a32)E32++(a31a13+a32a23+a332)E33
If A2=0 then
a112+a12a21+a13a31=0a11a12+a12a22+a13a32=0a11a13+a12a23+a13a33=0a21a11+a22a21+a23a31=0a21a12+a222+a23a32=0a21a13+a22a23+a23a33=0a31a11+a32a21+a33a31=0a31a12+a32a22+a33a32=0a31a13+a32a23+a332=0
This system has zero solution only aij∈Z .
So A2=0 .
Then M3[Z] has no nilpotent elements.
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