English
If c = a and d = b, then casting the segment from a to b yields the segment from c to d; endpoints are preserved under equality substitutions.
Русский
Если c = a и d = b, то приведение сегмента от a к b к сегменту от c к d сохраняет концы.
LaTeX
$$$ (Path.segment\ a\ b).cast (hac) (hbd) = Path.segment\ c\ d \text{ whenever } c=a\text{ and } d=b $$$
Lean4
@[simp]
theorem cast_segment {a b c d : E} (hac : c = a) (hbd : d = b) : (Path.segment a b).cast hac hbd = .segment c d := by
subst_vars; rfl