minimized imports

--- a/src/HOL/Multivariate_Analysis/Operator_Norm.thy	Sat Mar 29 12:05:24 2014 +0100
+++ b/src/HOL/Multivariate_Analysis/Operator_Norm.thy	Fri Mar 28 18:21:20 2014 -0700
@@ -6,7 +6,7 @@
 header {* Operator Norm *}
 
 theory Operator_Norm
-imports Linear_Algebra
+imports Complex_Main
 begin
 
 text {* This formulation yields zero if @{text 'a} is the trivial vector space. *}