TSum [(''Atag'', TPrim (Num U8)), (''Btag'', TPrim (Num U8)), (''Ctag'', TPrim (Num U8))] :=: t1
TSum [(''Btag'', TPrim (Num U8)), (''Ctag'', TPrim (Num U8))] :=: t2
TSum [(''Ctag'', TPrim (Num U8))] :=: t3