Section DsumRepr.
Variables (n : nat) (rG : reprG n).

Lemma mx_rsim_dadd  (U V W : 'M_n) (rU rV : representation)
(modU : mxmodule rG U) (modV : mxmodule rG V) (modW : mxmodule rG W) :
(U + V :=: W)%MS -> mxdirect (U + V) ->
mx_rsim (submod_repr modU) rU -> mx_rsim (submod_repr modV) rV ->
mx_rsim (submod_repr modW) (dadd_grepr rU rV).