... 2-formsat a point, dx 1 ∧ dx2, dx 1 ∧ dx3,anddx2∧ dx3,wheredx 1 ∧ dx2=dx 1 ⊗ dx2− dx2⊗ dx 1 , which means that, acting on u and v, dx 1 ∧dx2(u,v)=u 1 v2− u2v 1 . The product ... <ikωi 1 ikdxi 1 ∧···∧dxikover S bySω(k)=i 1 ,i2, ,ikωi 1 ik(x(u))k =1 ∂xi∂udu 1 du2···duk.Wehadbettergivesomeexamples. Fork = 1, the “surface” ... similarly for 1 a∂∂yi, which act on functionals of y(x)and ˙y(x)byδy(x 1 )δy(x2)= δ(x 1 − x2),δ ˙y(x 1 )δy(x2)=δy(x 1 )δ ˙y(x2)=0,δ ˙y(x 1 )δ ˙y(x2)= δ(x 1 − x2).Here...