| | Some definitions of interest. |
|
| append | Def as @ bs == Case of as; nil  bs ; a.as' [a / (as' @ bs)] (recursive) |
| | | Thm*  T:Type, as,bs:T List. (as @ bs)  T List |
|
| firstn | Def firstn(n;as) == Case of as; nil nil ; a.as' if 0 <  n [a / firstn(n-1;as')] else nil fi (recursive) |
| | | Thm* A:Type, as:A List, n: . firstn(n;as) A List |
|
| length | Def ||as|| == Case of as; nil 0 ; a.as' ||as'||+1 (recursive) |
| | | Thm* A:Type, l:A List. ||l|| |
| | | Thm* ||nil|| |
|
| select | Def l[i] == hd(nth_tl(i;l)) |
| | | Thm* A:Type, l:A List, n:. 0 n   n < ||l|| l[n] A |
