B = (0, 1)
c = Circle(B, 1)
C = Point(c)
D = Point(Circle[Midpoint[B, C], (Distance[B, C] * sqrt(3) / 2), Segment[B, C]])
a, A, faceABC, faceABE, faceBCE, faceACE, arêteAB, arêteBC, arêteAC, arêteBE, arêteAE, arêteCE = Tetrahedron(B, C, D)
M = Point(arêteBC)
N = Point(arêteAB)
α = Angle(M, A, N)
f = Segment(A, M)
g = Segment(A, N)
p: (Vector[A, M] * Vector[A, N])