[NTG-context] curly bracket different values (entries)

Hello, I am trying to get something like the x_n equation here (second one): http://latex.knobs-dials.com/images/47c5c3f63c4c9dcbdf4b4b4e362b01d00b8cb62b... but I am failing... this is my pathetic trial... any help would be appreciated. Thanks! \placeformula \startformula \phi^{N(n)}_m = \left{ \eqalign{ \phi^{R(n)}_m & {\rm inside the worldtube}\,, \cr \phi_m & {\rm outside the worldtube} \,, } \stopformula