TCHEBYCHEFF Documentation Error

[John Keith]

The HP 49/50 function TCHEBYCHEFF returns the nth Chebyshev polynomial of the first kind, given an integer n on the stack. The description in the AUR states that n must be a nonnegative integer. In fact, the function actually returns the Chebyshev polynomials of the second kind if given a negative integer argument. The polynomial returned is offset though, so that -n gives U(n-1, X).

Not sure if this is useful to anyone, but it's nice when a bug in the documentation reveals a hidden feature.