:: deftheorem Def41 defines -extending FOMODEL1:def 41 :
for S1, S2 being Language-like holds
( S2 is S1 -extending iff ( the adicity of S1 c= the adicity of S2 & TheEqSymbOf S1 = TheEqSymbOf S2 & TheNorSymbOf S1 = TheNorSymbOf S2 ) );