Japt: Approximating arccosine
It works, but it’s definitely not pretty.
Instead of falling back on the underlying language, we can brute-force a reasonable approximation:
ToMP1/7l¹ñ@McX aUÃv T // Take 0 o // and create a range from that MP // to π 1/7l¹ // with a resolution of 1/7!. ñ@ // Sort this range so that McX // the cosine of a given value aU // is closest to the default input `U`, Ãv // then return the first element.
The result is accurate to roughly four significant digits.