If X,Y are (matrix) generators of G => e^(tX),e^(uY) form one paramter subgroups of G.

g=e^(tX)e^(uY)e^(-ty)e^(-uy) in G = commutator of generators

d/dt(d/du(g(t,u)))|t=u=0 =[X,Y]

e^(v[X,Y])= another 1 parameter subgroup = a generator