I need a reference for the proof that the complex orthogonal group $SO_n($$SO_{2n+1}($ℂ$) = \{A\in GL_n($$) = \{A\in SL_{2n+1}($ℂ$): A^TA = Id\}$ is simple in a group theoretical sense (if it is true). How about the simplicity of $SO_n(K)$$SO_{2n+1}(K)$ in general (i.e. $K$ an arbitrary infinite field)? It there any criterion? It seems that if $K$ is "big", then $SO_n(K)$$SO_{2n+1}(K)$ is not simple, e.g. if $K$ has a valuation, then (I think) one can find somehow a proper normal subgroup.