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def definition def or abbrev

dir

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  32def dir (x y : R3) : R3 :=

proof body

Definition body.

  33  let v := (y - x)
  34  if h : ‖v‖ = 0 then 0 else v / ‖v‖
  35
  36/-- Angle at `x` between rays to `y` and `z`, defined via `arccos` of the inner product
  37of unit directions. Returns `0` if either ray is degenerate. Range is in `[0, π]`. -/

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