 The approximation error is measured in the norm of the isotropic Sobolev space W^{1,p \mathbb I%DIFDELCMD < }%%% ^d).
<fluency>  The approximation error is measured in the norm of the isotropic Sobolev space W^{1,p \mathbb I%DIFDELCMD < }%%% ^d).
 The approximation error is measured in the norm of isotropic Sobolev space W^{1,p \mathbb I%DIFDELCMD < }%%% ^d).