lista={{{2,1},{2,3}},{{4,1},{5,6}}}

lista[[2,1]]

MatrixForm[lista]

D[(x^2),x]

F=(1/(Sqrt[(x^2)+(y^2)])){x,y,0}
G=(1/(Sqrt[(x^2)+(y^2)])){y,-x,0}
f=(x^2)+(y^2)
grad[f_]:= {D[f,x],D[f,y],D[f,z]}
rot[A_]:={D[A[[3]],y]-D[A[[2]],z],D[A[[1]],z]-D[A[[3]],x],D[A[[2]],x]-D[A[[1]],y]}
div[A_]:=D[A[[1]],x]+D[A[[2]],y]+D[A[[3]],z]

rot[F]

Simplify[rot[G],Assumptions->{x∈Reals,y∈Reals}]

FullSimplify[rot[G]]

rot[f F]

rot[{0,z,-y}]

rot[{0,0,x}]

Simplify[div[F]]

div[G]

grad[f]

f