N.B. I have bitten the bullet, and I am going through Leonid Shifrin's "Mathematica Programming: An Advanced Introduction." (Which needs no introduction in this forum)
One question I have: could one establish that a symbol has a built-in rules, based on DownValues or related functions?
Unprotect[Sin] Sin[x_Integer] := Sin[N[x]] Protect[Sin] Sin (* 0.841471 *) DownValues[Sin] (* HoldPattern[Sin[x_Integer]] :> Sin[N[x]] *)
Hey, where are the built-in rules for Sin?