| | Who Cites segment? |
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| segment | Def as[m..n ] == firstn(n-m;nth_tl(m;as)) |
| | | Thm*  T:Type, as:T List, m,n: . (as[m..n])  T List |
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| nth_tl | Def nth_tl(n;as) == if n  0 as else nth_tl(n-1;tl(as)) fi (recursive) |
| | | Thm* A:Type, as:A List, i:. nth_tl(i;as) A List |
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| 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 |
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| tl | Def tl(l) == Case of l; nil nil ; h.t t |
| | | Thm* A:Type, l:A List. tl(l) A List |
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| le_int | Def ij ==  j < i |
| | | Thm* i,j:. (ij)  |
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| lt_int | Def i < j == if i < j true ; false fi |
| | | Thm* i,j:. (i < j) |
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| bnot | Def b == if b false else true fi |
| | | Thm* b:. b |
