Section Euclid.
Context `{Ax:euclidean_neutral_ruler_compass}.

Lemma lemma_angleaddition :
forall A B C D E F P Q R a b c d e f p q r,
SumA A B C D E F P Q R -> CongA A B C a b c -> CongA D E F d e f -> SumA a b c d e f p q r ->
CongA P Q R p q r.