== inr(inl(
)) 
case0; 3 case1; 3
case2; == InjCase(x; zero. case0; one_or_two. InjCase(one_or_two; one. case1; two. case2))
t:Type{i}, t':Type{j}, t'':Type{k}, c:t, c':t', c'':t''. case 3: 3 c; 3 c'; 3 c''; tt:Type{i}, t':Type{j}, t'':Type{k}, c:t, c':t', c'':t''. case 3: 3 c'; 3 c''; 3 c; t''t:Type{i}, t':Type{j}, t'':Type{k}, c:t, c':t', c'':t''. case 3: 3 c; 3 c'; 3 c''; t''
