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(*    Contraction                                                             *)
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(* Specifications: *)
Lemma contraction_v0  (a b c d e: point) :
('[a, b, c] * '[a, d, e] + -(1) * '[a, b, e] * '[a, d, c] =
'[a, b, d] * '[a, c, e])%f.
Lemma contraction_v1  (a b c d e: point) :
('[a, b, c] * '[b, d, e] + -(1) * '[a, b, e] * '[b, d, c] =
'[a, b, d] * '[b, c, e])%f.
Lemma contraction_v2  (a b c d e: point) :
('[a, b, c] * '[d, b, e] + - (1) * '[a, b, e] * '[d, b, c] =
'[b, a, d] * '[b, c, e])%f.
Lemma contraction_v3  (a b c d e: point) :
('[a, b, c] * '[d, a, e] + - (1) * '[a, b, e] * '[d, a, c] =
'[a, b, d] * '[c, a, e])%f.