Thm* L:LangOver(Alph). (L0) = lang_zero_power
Thm* L:LangOver(Alph). (L) = L lang_sing_prod
Thm* L:LangOver(Alph). (L) = L lang_prod_sing
L:LangOver(Alph). (L
0) = 
lang_zero_power
(l) == null(l)
L:LangOver(Alph). (L0) = lang_zero_power
L:LangOver(Alph). (
L) = L lang_sing_prod
L:LangOver(Alph). (L) = L lang_prod_sing