dimUnion :: Dimensions -> Dimensions -> Dimensions
dimUnion (D t r b l) (D t' r' b' l') = D (min t t') (max r r') (max b b') (min l l')
dimUnion :: Dimensions -> Dimensions -> Dimensions
dimUnion (D t r b l) (D t' r' b' l') = D (min t t') (max r r') (max b b') (min l l')
dimUnion (D t r b l) (D t' r' b' l') = D (min t t') (max r r') (max b b') (min l l')